3.14.1 The landing sequence In this module we will look at the common factors to be considered in landing a normally configured, three-axis, fixed-undercarriage, nosewheel or tailwheel aircraft, which may or may not be flap-equipped. Aircraft designed with full 'short take-off and landing' [STOL] capability will use slightly different techniques in some parts of the approach and landing. There are differing landing procedures or techniques, or combinations thereof, applicable to airfield dimensions and surface conditions: normal landing short-field landing soft-field landing. The basic landing sequence is varied, according to prevailing conditions (and there is a varying degree of alignment correction to allow for the crosswind component of the wind velocity), but it usually has four parts: Joining the circuit pattern of the airfield, during which the aircraft is decelerated from cruise speed to circuit speed, the airfield is visually checked for serviceability and obstructions, surface wind direction ascertained from observation of the windsock(s), the whereabouts of other traffic is established, the landing direction and approach is planned and the pre-landing cockpit checks are carried out in a logical sequence. The approach to the landing, during which the aircraft is decelerated from circuit speed to the reference indicated approach speed [Vref], configured for landing, then finally stabilised at a constant speed and rate of descent with wings level and aligned — so that the flight path traced over the ground, during the final approach, is on the same line as the intended ground roll-out path. The stabilised approach should be established before the aircraft is at a height 300–400 feet above the runway/airstrip/landing area. Once established, only slight movements of the flight and engine controls should be necessary to maintain the approach. The flight path passes over an imaginary 50 feet high screen, placed at a short distance before the airstrip threshold. A transition period, where both the rate of descent and the forward speed are slowed during a 'round-out' or 'flare' prior to touchdown. The touchdown and subsequent ground roll, after which the aircraft is turned off the landing area at an appropriate taxiing speed. The arrival is complete when the aircraft is properly parked, the engine is properly shut down, any passenger is safely disembarked and the aircraft is secured. The most favourable conditions for optimum landing performance at, or near, maximum weight are: a pilot who exercises sound judgement, and follows the rules and recommended procedures a surface of ample length, which is dry and level, or with a slight upslope a low density altitude; i.e. low elevation and low temperature a smooth, full headwind of reasonable and constant velocity. 3.14.2 Factors affecting safe landing performance Apart from the pilot's physiological condition, airmanship, experience and capability — and the aircraft's weight and balance condition — landing performance is limited by the following constraints, all of which should be carefully assessed — both within the pre-landing procedure and at the flight planning stage — to establish whether a safe landing is viable. Generally most of the engine effects and other constraints affecting take-off performance, covered in section 11.3, have no significant effect on landing performance — except, with both tailwheel and nosewheel aircraft, the inertial effect of the cg position. However, when a landing attempt is aborted, then any of those constraints may be present during the initial go-around. Demonstrated landing distance. Landing distance is the total distance required to clear an imaginary screen, 50 feet (or 15 metres) high, placed before the airstrip threshold; then touch down and bring the aircraft to a halt with normal braking — in nil wind conditions. It should be borne in mind that the manufacturer's 'demonstrated' landing distance has been achieved by a very experienced test pilot in very favourable conditions, during the type certification tests. The landing distance required by the average recreational pilot may be considerably greater. Airfield dimensions and slope. The usable length of runways or strips must be ascertained, as well as the degree of slope — both with and across the direction of landing. Landing downslope will reduce deceleration and lengthen the ground roll. Slope across the landing path makes the touchdown and subsequent ground roll more difficult to control. At a 'one-way' airstrip a combination of airfield slope and rising terrain at the high end necessitates landing upslope, no matter what the wind direction. Airfield surface and surrounds. A short, dry grass or rough gravel surface might decrease the ground roll by 10% compared to that for a smooth, sealed surface. Wet or long grass might decrease the ground roll by 30%. However, there is a possibility that a wet surface can induce aquaplaning/hydroplaning, which adversely affects braking and/or can result in a ground loop (where the aircraft suddenly swings through 180° or more with probable undercarriage and propeller damage). Frosty grass provides little friction, so be wary in early morning shadowed terrain. Long grass and weeds can catch a wingtip, resulting in a ground loop. A soft or waterlogged surface might greatly decrease the ground roll but will increase the possibility of the aircraft tipping over during the ground roll, or may delay — or even prevent a take-off — if such is attempted during the landing ground roll. The location and height of constructed obstructions, trees and local topography must be assessed. Airfield density altitude. This is a critical factor that is often not correctly assessed. High density altitude has a major effect on the approach speed (i.e. the true airspeed is significantly greater than the indicated airspeed), and thus the ground speed at which the aircraft touches down and the length of the subsequent ground roll. High density altitude also affects the aircraft's climb-out performance if the landing is aborted. Re-read the section on high density altitude. Wind velocity and turbulence. Wind strength, direction, downflow, gust intensity, surface turbulence and the potential for wind shear events are normally the major considerations in landing performance. Read the micrometeorology turbulence module, but particularly the section on 'lee wind downflow and eddies'. You should also read the CASA Advisory Circular 'Safety during take-off and landing'. This is an abridged web version for recreational aviation. The pilot-in-command of an aircraft must assess all the foregoing factors and conditions to ascertain the total distance required for obstacle clearance and landing, judge if the landing can be conducted safely and ascertain a safe go-around route if the landing should need to be aborted. All the foregoing assumes that the height of the cloud base allows sufficient visibility, and appropriate terrain and obstruction clearance within the circuit. The problem for the less cautious pilot — if the airfield conditions are found to be unsuitable — is that an eventual landing is mandatory and, if flight planning is poor, there may be no acceptable alternate airfield within range. 3.14.3 The standard circuit pattern For at least the past 65 years, a standard procedure has been adopted for any piston-engine light aircraft approaching to land at a non-controlled public airfield. This procedure is called the standard circuit pattern and is adopted by convention rather than laid down by regulation. Following the pattern requires that an aircraft should track over at least three legs of a rectangular course aligned with the runway or landing strip that is most into-wind. Turns, once established within the circuit, will all be in the same direction, usually to the left unless terrain or ground habitation dictate otherwise. The downwind leg will be flown at moderate speed (adjusted to avoid overtaking preceding aircraft) and at a constant height — normally 1000 feet above the airfield level is recommended, but some primarily ultralight airfields may have a lower standard circuit height. And, of course, the aircraft must be operating in visual meteorological conditions [VMC] — clear of cloud and in sight of the ground at all times, if at or below 1000 feet agl. Check the visual meteorological conditions for aircraft operating under the visual flight rules. Consistency The height of the circuit is particularly important for ultralight pilots. Ultralight engines and associated systems are not renowned for their reliability and the circuit height should be sufficient that, following power loss, an aircraft flying a reasonably tight circuit has every chance of gliding to a safe landing area on the airfield. Pilots should adopt their own personal circuit procedures, to be used wherever possible; the principle being that consistency improves performance. Do not automatically apply the procedure utilised at a training airfield when operating elsewhere. The skills involved can only be assimilated by repeated practice at many airfields — not by reading books or web pages. Consistency is the key. Every circuit and landing should be performed to the best of the pilot's ability; such consistency makes the occasional difficult landing easy. The diagram below (adapted from the Sydney Basin Visual Pilot Guide, courtesy of the Australian Civil Aviation Safety Authority's Aviation Safety Promotion program) demonstrates the full routine for a piston-engine aircraft inbound for landing at a public airfield. The routine 1. The first stage is an overflight at a height not less than 1500 feet agl (preferably with Local QNH set, but if this is not obtainable, use Area QNH) to determine the airfield serviceability, the surface wind direction, the runway/strip being used by other traffic and confirmation of the circuit direction; or if no other traffic, to select the strip to be used. While in the circuit, keep monitoring the relative position and the movements of other traffic at all times. Note that the 'circuit area' is taken to cover the area within a radius of three nautical miles from the 'airfield reference point'. Assume that the latter is the runway intersection. If the airfield is unfamiliar, the overflight also provides the opportunity to examine the circuit area for safe escape routes from each runway following a late go-around. Also check the area for suitable forced landing sites and associated hazards should the engine fail during a go-around or after take-off. See the Coping with Emergencies Guide. 2. The second stage is to manoeuvre so that a let-down from 1500 feet is commenced on the 'dead' side of the active runway, tracking close and parallel to that runway. This is the upwind or into-wind leg. The first and second stages provide the opportunity to carefully check the airfield area and boundaries for hazards — animals, power lines and other wires, ditches, obstructions, and to ascertain the whereabouts of other traffic in, or joining, the circuit and to be seen by them*. All manoeuvring should be done so that the airfield activities always remain in sight; i.e. don't turn away for a short time and then follow with a reversed turn onto downwind. *The official term for this latter procedure is 'unalerted see and avoid', but it has its limitations. See the Australian Transport Safety Bureau research report 'Limitations of the see-and-avoid principle'. The report was first issued in 1991 when mid-air collisions in Australian general aviation averaged about one per year but collisions have increased slightly since then. Most — or nearly all — general and powered recreational aviation mid-airs occur in the circuit area, generally when one aircraft descends into another from behind. 3. When circuit height is reached and the upwind end of the runway has been passed, choose an appropriate position to turn onto the crosswind leg so that there will be no conflict with traffic on the crosswind and downwind legs, and to achieve optimum traffic spacing. You are now entering the traffic side of the circuit. Watch for aircraft joining the circuit on crosswind and for aircraft taking off; ensure that you provide adequate clearance. Maintain circuit height and, allowing for drift, track at 90° to the runway. 4. Turn 90° onto the downwind leg at an appropriate distance past the runway (after checking for aircraft joining the circuit on the downwind leg), check the crosswind drift against selected landmarks and adjust heading to track parallel to the runway, perform the appropriate downwind cockpit checks, and hold altitude and appropriate traffic spacing. Set power and trim the aircraft to maintain an airspeed that allows time to plan the landing without unnecessarily delaying other traffic — probably around 1.7 × Vso. Note: although we call these legs 'upwind', 'crosswind' and 'downwind', they are only nominally named so, because the surface wind is unlikely to be closely aligned with the 'into-wind' runway — particularly with a single strip — and the wind at circuit height might vary considerably from that at the surface. 5. Planning time! Pick an intended touchdown target on the airstrip. This should be far enough into the strip so that an undershoot on approach will still allow normal roundout and touchdown on the runway, or an overshoot on approach will still allow ample runway to bring the aircraft to a halt. For all ultralights and most light aircraft, the latter requirement is probably inconsequential for most runways at public aerodromes. A touchdown target maybe 400 feet from the threshold is about the norm; never target the beginning of the runway or strip for touchdown. Now choose another point, say 200 feet back from the touchdown target towards the threshold; this is the aiming point. Of course, it may be difficult to identify such positions at a featureless airstrip; also, the figures will vary according to the aircraft's drag characteristics in the landing configuration. We are presuming here that we are operating at the average recreational aviation airfield where the strip length may be 2000–3000 feet. It can be a little embarrassing for the light aircraft pilot who touches down 400 feet past the threshold of a 6000 feet runway and then has to taxi a kilometre to the next exit. At a certified aerodrome, the runway centre-lines are 100 feet [30 m] long with a 100 feet gap in between, and the 'piano keys' which normally mark the threshold are also 100 feet long. There should also be touchdown marks at 500 feet [150 m], 1000 feet [300 m] and 1500 feet [450 m]. 6. At an appropriate distance past the aiming point, turn 90° onto the base leg, and hold airspeed but reduce power so that a descent is started during the turn. Lower the first stage of flap if so equipped. Reduce airspeed (but not less than 1.5 × Vso), and trim. The time spent flying base leg is most important, as it provides the opportunity to: set up the aircraft in the approach attitude; establish a power and flap setting (and trim) for the required rate of descent; check for conflicting traffic both airborne and on the ground and particularly any traffic on a straight-in approach or very wide circuit; assess the crosswind component along the landing path; decide the touchdown technique appropriate for the conditions; and review the pre-landing checks. Hold an accurate heading on base to carefully monitor drift, comparing the wind velocity at that height with the surface wind indicated by the windsock(s). A significant difference between the two indicates wind shear will be encountered during the final approach — this may erode the safety margin between the approach speed and Vso, or cause other difficulties. Never be tempted to fly a semi-circular base with a short final approach — it is very poor airmanship and negates all the safety check features of the square base leg. It may be that preceding traffic conditions preclude a turn onto base at the optimum position — in which case you must reduce speed and/or extend the downwind leg further downwind; maintain altitude; and delay the start of descent, and some actions, until the aircraft is well into the base leg or even established on final approach. 7. Start a 90° descending turn onto the final approach so that, on completion of the turn, the aircraft is lined up with the extended notional centre(line) of the landing strip. During the turn, be aware of the reversal height phenomena and confine external scanning to the intended flight path and to the check for conflicting aerial traffic particularly ahead of and behind you. Watch for aircraft on or near the runway; if in doubt about safety initiate a go-around. If satisfied with the initial approach, then lower full flap (if the wind speed is fairly high, then partial flap may suffice), adjust airspeed to the recommended final approach speed [Vref] and re-trim. Once stabilised in the final approach, control the airspeed and the rate of descent with small movements of flight controls and throttle. The power setting should be such that it allows small power reductions, or power increases, in order to maintain the approach path. This can't be done if the approach is set up with the engine at idle power. In addition, the thrust response is not that effective from an idle setting and, for many aircraft, an approach at idle power will entail a high sink rate, which may be difficult to manage. Also, an idle power approach tends to over-cool the engine and may promote carburettor icing, both of which may result in high power not being available when needed — such as in a go-around. If flying an aircraft with a low approach speed into a relatively high wind************* 8. Continue tracking down 'final', whilst correcting for the crosswind component, and watching the position and apparent movement* of the aiming point relative to the windscreen. Then at 50 feet or so, substantially reduce the rate of descent, reduce thrust to zero, touchdown and roll-out until it is safe to turn off the landing strip. If so equipped, and in a nosewheel aircraft, brakes may be applied to slow the aircraft during the latter part of the roll-out — but only if the aircraft is moving in a straight line on a firm surface and the elevators are raised to keep excess weight off the nosewheel. In a tailwheel aircraft, be very wary of any brake application during the roll-out. The braking systems in ultralight aircraft are generally only provided for light use in ground manoeuvring. * If the aiming point appears to be moving up the windscreen you are undershooting (too low) and will touch down before the target. If the aiming point appears to be moving down the screen you are overshooting (too high) and will touchdown past the target. If it appears to be motionless in the screen the approach slope is good and touchdown will be close to the target. The foregoing presumes that all of the runway is visible through the windscreen during the final approach. However, there are some aircraft where the forward visibility over the nose is inadequate at approach speeds and special techniques, such as side-slipping, may be required. Variations on joining the circuit The previous discussion outlined the full circuit pattern that should be adopted when inbound to an unfamiliar airfield. However, when inbound to a familiar airfield of which you are aware of the current runway in use and its serviceability, it may not be necessary to overfly the airfield, and the circuit may be joined anywhere on the green path; i.e. on the upwind, crosswind or downwind leg. Downwind joins are normally made at a 45° angle from outside the pattern. You should not join the standard circuit on base or final — the red shaded path in the diagram. When joining crosswind or downwind, you should already be at the circuit height. Note that only the pattern of the standard circuit is fixed. Its dimensions; e.g. the length of the downwind leg or its distance from the runway, are variable. It is good practice to fly a nice, tight circuit. This also allows a forced landing to be accomplished safely on the airfield if power is lost. However, for operational reasons, not all aircraft will fly a standard pattern or even base their circuit on the same runway. The turning radius of regular passenger transport [RPT] aircraft is too large to conduct the normal circuit pattern, so they perform either a 'circling approach' or a 'straight-in approach'; the latter being much safer for RPT aircraft. Agricultural aircraft reloading at a public airfield tend to use a runway and circuit pattern which best suits the job conditions. CASA have produced two new (2010) advisory publications to support procedures and provide guidance on a code of conduct to allow greater flexibility for pilots when flying at, or in the vicinity of, 'non-towered' aerodromes; i.e. airfields in Class G airspace. These Civil Aviation Advisory Publications are: CAAP 166-1 'Operations in the vicinity of non-towered (non-controlled) aerodromes' and CAAP 166-2 'Pilots responsibility in collision avoidance in the vicinity of non-towered (non-controlled) aerodromes by 'see and avoid'. Please read the combined CAAP 166-1/166-2 document. Note that the 'ultralight' term used in the CAAPs when recommending a 500 feet circuit height, refers only to those RA-Aus aircraft which have a normal cruising speed below 55 knots, or thereabouts. CASA have also produced an online interactive learning tool titled 'Operations at, or in the vicinity of, non-towered (non-controlled) aerodromes' which is now available at casaelearning.com.au/M02/index.htm. 3.14.4 Non-standard circuits Special procedures for joining on final apply at non-towered aerodromes. Aircraft joining for a straight-in approach should be established on the straight-in approach heading by not less than three nautical miles from the airfield; in addition, the aircraft's landing lights and anti-collision lights must be switched on. The straight-in approach option is available to any aircraft (though not recommended) but should only be utilised by aircraft whose approach speed is much higher than the norm; e.g. RPT aircraft. An aircraft on a straight-in approach must give way to aircraft already reported established on base or final approach. The straight-in approach is often made on the longest runway, not necessarily the into-wind runway. Joining on the base leg is also available but not recommended. Refer to the procedures section of the VHF radiocommunications guide for the standard broadcasts on the CTAF. Operational need and the pattern flown The following extract from an older Australian Civil Aviation Safety Authority Advisory Circular AC 91-220(0) concludes that "Safety rules permitting, the pilots of each type of aircraft will want to fly the circuit pattern most suited to the aircraft and the type of operation. Pilots have to give and take relevant information and exercise tolerance and consideration if varied circuit flight paths and experience levels are to be accommodated safely." Extract from that draft AC 91-220(0) regarding operations at non-controlled aerodromes. The principal factors or elements relating to operations in VMC are: The type of operation — agricultural, pilot training, air transport Type of aircraft Wind speed and direction Number of runways Obstructions and topography in the vicinity of the aerodrome Built-up areas and local noise sensitivity Number of aircraft Other activities — parachuting, glider flying, flight training Whether all aircraft are radio-equipped and proximity of controlled airspace and low-level operations Non-communicating traffic and non-compliant traffic. There can be varied operational needs and manoeuvres conducted at a non-controlled aerodrome: Skilled pilots will often want to make smaller circuits than pilots under training or with low recency Larger air transport aircraft are expensive to run, and minutes saved make straight-in approaches an attractive proposition Helicopters are not restricted to normal circuit patterns and generally operate to stay clear of fixed-wing circuit patterns Pilots doing actual or practice instrument approaches will often make straight-in or abbreviated approaches to a landing or to a missed approach point on an instrument runway, or will elect to join the circuit from overhead a navigation aid via the most convenient turn to the runway in use Agricultural pilots conducting local deliveries may prefer to do a contra or a low-level circuit, or make straight-in approaches on a cross runway (expect any legitimate manoeuvre that will speed up delivery rates) Parachuting and glider tug aircraft may make steep descents into the circuit area Ultralight pilots generally prefer to make low, small circuits, and to overfly terrain with potential for a safe forced landing Gliders require winching or towing, often use parallel runways and/or contra circuits, and are committed to land from the time they enter the circuit Trainee pilots require relatively large circuits, don't have reserve capacity to cope with unusual manoeuvres by other aircraft , and can easily be forced to abandon their preferred flight path by other aircraft, including those on normal manoeuvres. Though a little out=of-date the complete CASA draft advisory circular 91-220 (0) makes useful reading and has been provided on this site as 'Operations at non-controlled airfields. 3.14.5 Final approach slope and duration Large aircraft on the final approach to the runway normally descend along a documented path which is inclined at about 3° to the horizontal and aligned with the runway. All Instrument Landing Systems [ILS] are based on this 3° (or 5%) approach slope; the term glideslope is usually accepted to refer to the approach slope in such systems. Most of the secondary aerodromes in Australia are equipped with the ground aid Visual Approach Slope Indicator systems [VASI], or something similar; these day and night optical indicator systems also utilise the 3° glideslope. Thus for larger aircraft, the approach technique is to intercept the glideslope some distance from the runway threshold and to maintain a consistent airspeed and rate of descent throughout the straight-in approach. The rate of descent necessary to maintain the glideslope is controlled by slight power changes and depends on the effect of wind; i.e. the ground speed. The rule of thumb for the required rate of descent in feet per minute along a 3° slope is the ground speed in knots multiplied by 5. This is just another application of the 1-in-60 rule. One knot = 100 feet per minute, so if the ground speed is 120 knots (12 000 ft/min) the rate of descent required to maintain the slope is 12 000 × 3/60 = 600 ft/min. If a 20 knot wind reduces the ground speed to 100 knots, the rate of descent required reduces to 500 ft/min. Maintenance of the glideslope and direction (the track over the ground should follow the extended runway line) are the critical needs in a precision approach. Thus it is also necessary to assess the crosswind component of the wind velocity and make the necessary heading adjustment to compensate for drift. Light aircraft approach slope and speed For light aircraft approaching at a ground speed of, say 50 knots, the 3° slope is not really practical as the rate of descent required would be only 250 ft/min. This extends the time spent on final which, in turn, tends to back up the traffic in the circuit. Also, maintenance of a documented approach slope is not a critical need in an approach that is not instrument, GPS or ground aid oriented. Glideslope management for light aircraft entails a bit of mental arithmetic to either: calculate the rate of descent required plus monitor the VSI — if fitted, or if more comfortable with a particular rate of descent, calculate the ground distance necessary between aiming point and final approach point (see below). Light aircraft generally use a steeper approach slope — maybe around 6° which, at 50 knots ground speed, would require a rate of descent of 500 ft/min. The rule of thumb for the rate of descent to maintain a 6° slope is the ground speed in knots multiplied by 10 equals the rate of descent in feet per minute. The manufacturer's recommended final approach speed [Vref] chosen for light aircraft in normal approaches is usually not less than 1.3 × Vso, possibly 1.5 × Vso for low speed aircraft. (The slower the aircraft, the greater the effect of atmospheric turbulence.) The planned rate of descent is usually established by pilots as one they are comfortable with, at the final approach speed. Airspeed and the rate of descent, at a particular flap setting, are controlled by small adjustments in attitude and power. Sideslipping adds another dimension to the approach angle. You should review 'forces in a descent' and the 'lift/drag ratio'. For a normal approach it is important to hold — and trim the aircraft into — the recommended approach speed without adding any extra 'safety factor'; the safest approach and landing will be achieved at that recommended airspeed. An allowance for wind gusts should be added if necessary, or 2–3 knots may be added in significant crosswind conditions (see below). The duration of the final approach then depends on the height from which 'finals' are commenced and the planned rate of descent. In a normal approach, the final approach is usually started at about 400–500 feet agl with a chosen rate of descent around 400–500 feet per minute; thus the time on final should be about one minute. The over-the-ground distance covered during final approach depends on the duration, the approach airspeed and wind velocity. Taking a low momentum ultralight approach as an example, if the turn onto final is completed at 500 feet agl, the rate of descent is 500 ft/min, the approach speed is 50 knots and the headwind velocity is 10 knots, then the ground speed is 40 knots (4000 ft/min), the duration is one minute and the final approach must start about 4000 feet from the aiming point. The lower the ground speed (as with a stronger headwind), the lesser the ground distance must be between start of final and the aiming point, otherwise you end up conducting a low 'drag it in' approach. This is not good energy management,as it is both low and slow — and totally reliant on engine power to keep you out of trouble. It is probably unwise to use full flap when confronted with high wind speed on the approach because, under the conditions just described, you will be flying the back of the power curve with significant power required to balance the increased flap drag; it is better to choose a flap setting that provides a higher CL without a substantial increase in CD. Final approach point Having chosen the rate of descent, the height at which the final approach will commence and estimated the wind velocity, then sometime during the downwind leg the pilot must determine the ground position that marks the final approach point — the point where the turn from base onto final will be complete. The position at which the preceding 90° descending turn — from downwind onto base — should be commenced is determined by that final approach point and the wind velocity. Presuming that the wind direction at circuit height is roughly aligned with the landing direction, then the higher the wind speed, the earlier the turn onto base must be started. Allowing for crosswind When the aircraft is flying the upwind, downwind or base legs, the allowance for drift — in order to maintain a tidy rectangular track around the circuit — is always accomplished by assessing the necessary wind correction angle or crab angle and adjusting the aircraft's heading so that the aircraft 'crabs' along the required ground line. The crab method is also used on final approach, particularly in larger aircraft, to adjust for the crosswind component. Rudder, rather than aileron, is used to make small adjustments to the aircraft heading. The crab method is the most comfortable for passengers. However, the forward slip method is probably easier to manage in some light aircraft if the crosswind component becomes significant on final approach. The main thing in handling crosswind is to ensure that the aircraft is not moving sideways at touchdown; i.e. the longitudinal axis is aligned with the direction of forward movement and that direction should preferably be aligned with the runway or strip. Sideways movement at touchdown stresses the undercarriage and may prompt a violent swing. In an ultralight, if the crosswind component is becoming a bit extreme you can always reduce it a bit by landing diagonally (i.e. edge to edge) across a (wide) runway or strip. The crosswind component and its relativity to aircraft speed will vary as the aircraft descends due to the decreasing wind gradient and the reductions in aircraft speed. Particular care should be taken when landing upslope, as the wind speed might drop off very rapidly near the surface, due to the blanking effect of the terrain. 3.14.6 Flare, touchdown and ground roll During the final approach, the aircraft should be descending towards the aiming point. Maybe a few seconds before it will fly into that point, the aircraft is 'flared' so that the aircraft's attitude is smoothly changed — from the nose-down attitude of the approach to a nose-high attitude for landing. During this 'round-out' transition period, power is smoothly reduced to idle, or near idle, and the aircraft's vertical speed is reduced from maybe 400–500 ft/min to practically zero. At the same time, its forward speed is also reduced from the approach speed to about 1.15 × Vso, plus any wind gust allowance. Because the aircraft is turning in the vertical plane, wing loading will increase during the flare so stall speed during that period will be slightly above Vso. If the flare elevator pressure is excessive, the aircraft will 'balloon'; i.e. the nose will point skyward and airspeed will drop off very rapidly in a (very) short climb unless immediate corrective action is taken. At the end of the flare manoeuvre, the aircraft should be flying level just above the surface and decelerating as it approaches the touchdown target. An aircraft close to the surface will be in ground effect and the decreased induced drag will mean that the rate of deceleration slows; i.e. the aircraft will tend to 'float'; the higher the ground speed, the longer the float duration, and the greater the chance of encountering some difficulty due to wind gusts, lulls or shifts. If you approach with a tailwind, the aircraft will seem to float forever. The drag from fully extended flaps will increase deceleration and reduce float. The duration of the float will be minimised by an approach at the correct airspeed plus a firm, smooth round-out and power reduction. The touchdown airspeed chosen by the pilot depends on wind conditions, and there are two touchdown options. The usual technique is for the pilot to ease the main wheels onto the surface while finally closing the throttle, touching down lightly while the aircraft is in a somewhat nose-high attitude but still above Vso — a 'wheeler' landing. This technique is always used in unfavourable wind conditions. Sometimes, rather than the pilot flying the aircraft onto the surface, the aircraft might be held in that attitude just above the surface until airspeed decays and the aircraft lands itself. At touchdown — in a taildragger only — some forward pressure may be applied to the control column until the speed decays below Vso, pegging the aircraft down with the reduced aoa so that it cannot lift off again, while airframe drag and wheel friction are slowing the aircraft. A nosewheel aircraft should never be allowed to touch down nosewheel first, or the nose and main wheels together, as wheelbarrowing may result. The nosewheel should be held off the surface during the roll out until the aircraft slows, and then gently lowered, rather than letting it drop down of its own accord. Keep the aircraft aligned with rudder. The alternative technique is to 'hold-off' the touchdown by gradually increasing control column back pressure, and holding the wheels a few centimetres above the surface as the airspeed decays. Recalling the formula: Lift = CL × ½rV² × S, you can see that in this technique the pilot is preventing the aircraft from touching down,and holding lift constant by increasing CL as V² reduces. When close to the stalling aoa and the airspeed is near Vso, the pilot stops increasing back pressure and the aircraft sinks, alighting smoothly in a nose-high attitude. This technique is particularly suitable for tailwheel aircraft — but only in favourable wind conditions. The object is to touch down simultaneously on the main wheels and tailwheel; i.e. a 'three-point' landing, without the aircraft sinking very far. When using this technique in a nosewheel aircraft you must not allow the nosewheel to thump down when the main wheels touch. If the 'crab and kick' technique is used to compensate for crosswind, then the aircraft's fore and aft axis must be finally aligned with the direction of movement by kicking the rudder just before touchdown occurs; good timing is necessary. After touchdown maintain runway alignment with rudder. A refinement, requiring a very fine touch on the controls, is to crab until very close to the runway then gently lower the into-wind wing so that the main landing gear on that side contacts the runway, then using rudder, pivot on that wheel to align with the runway centre-line. Similarly, if the forward slip method is used, then touchdown is made on the into-wind main wheel before the airspeed decays below Vso. The weight should be kept on that wheel until the aircraft slows at which stage the other wheel will contact the surface. If a nosewheel is interconnected to the rudder pedals for ground steering — and it remains connected even if the weight is off the nosewheel strut — then the nosewheel will be deflected in flight by the use of rudder. Touchdown of a deflected nosewheel must be avoided so the rudder must be in the neutral position before the nosewheel is lowered to the surface. During roll-out in crosswind conditions, the into-wind aileron is raised to prevent that wing from lifting — if gust-effected — and direction is controlled with rudder. In a taildragger, the pilot must be prepared to counter the inertial effect of the centre of gravity position. Unless there is a good reason for doing so — a touch-and-go landing, for example — flaps should not be raised until the aircraft has reduced to taxiing speed or turned off the landing strip. If there is some distance to taxi, then before turning off, it is safe practice to move to the side of the runway from which you will turn, to leave room for another aircraft — just in case. Soft field technique If the airfield is soft then the technique is to minimise the weight on the main wheels at touchdown, gradually transferring the weight from wings to main wheels as the aircraft slows. The approach is normal, using full flap if available, and the aircraft is flared as normal for a reasonably nose-high attitude — but a little power is applied just before touchdown, as you feel for the surface. Be prepared for the aircraft nose to pull down hard as the wheels sink — the same nose-down pitch will happen if touching down in long grass, particularly if it is wet. Remove the power smoothly, do not touch the brakes (a locked wheel will not ride over any obstruction), hold the control column well back and keep the aircraft moving until you attain firm ground. The rebound effect The rebound effect following a heavy, main wheel landing differs between tailwheel and nosewheel aircraft. A taildragger's cg is behind the main wheels, while a nosewheel aircraft's cg is in front of the main wheels. Thus the inertial effect combined with the reaction forces generated by the tyres and shock-absorber gear of a taildragger — acting vertically ahead of the cg — will tend to rotate the aircraft nose-up during any rebound, thereby increasing the aoa and thus lift. The aircraft bounces high, induced drag increases and a series of bounces or even pilot-induced oscillations could be initiated. The possibility of a stall with wing-drop is high. The opposite effect occurs with a tricycle gear aircraft; the rebound effect will tend to rotate the aircraft nose-down, reducing aoa and lift and thus bringing the nosewheel closer to the surface; the initial bounce is mild and any subsequence bounces might be described as skip-bounces; the chances of wheelbarrowing increase. Recovery from a bad bounce is probably best achieved by going around if safe to do so, otherwise by adding a little power and easing the aircraft into the proper condition for a smooth landing. 3.14.7 Going around A go-around is a decision to abort the landing and climb straight ahead (perhaps to rejoin the circuit on the crosswind leg), and involves a transition period between the descent phase and subsequent climb. A go-around decision might be taken at any time during the final approach, the flare, or sometimes even after initial surface contact. If the decision is made late, then the transition period might be a critical time for the pilot because of the low energy status of the aircraft and its low-speed flight characteristics. For lower-powered aircraft, the go-around technique requires a full, smooth application of full-throttle power to arrest the descent (followed by checking carby heat control to cold air and, if fitted with variable pitch propeller, ensuring pitch is set to maximum rpm), then maintain level flight while building kinetic energy or perhaps even trade some height for faster acceleration. Only commence the climb-out when Vx, Vy or an intermediate climb speed is attained. If the aircraft is low when the go-around decision is made and power is applied, then continuing to descend so that the aircraft can be accelerated in ground effect will provide some additional airspeed should that be considered safe and desirable. There may be occasions when a cooled (or iced-up) engine fails to respond to the throttle being opened in a go-around following a throttled-back glide approach or a practice forced landing approach. (The same lack of response may occur if the throttle is opened too rapidly.) Consequently, the pilot should be careful not to raise the nose before, or at the same time as, opening the throttle because — if the engine doesn't respond, there will be no increase in thrust to balance the substantially increased drag; sink rate will increase and the wings will approach the critical aoa. Generally, the aircraft will pitch up with full application of power and it should not be necessary to apply very much control column back pressure, but raise the nose AFTER the engine has responded properly. If the aircraft is equipped with flaps, then the flap retraction procedure for a go-around should be specified in the pilot's operating handbook. Generally, to avoid dangerous sink, flaps should be raised slowly in stages — and only when a positive climb rate is established, and obstacles are cleared — then finally cleaned up when a safe height is reached. Some aircraft will not climb at full throttle with full flap deflection (this particularly depends on gross weight, cg position and density altitude but perhaps is further complicated by rising terrain) in which case it is necessary to reduce to an intermediate flap setting during the transitional stage of the go-around, while applying just sufficient control column back-pressure to negate the sink. If climbing with approach flaps extended, the aircraft's attitude in pitch may differ substantially from the normal climb attitude. If a go-around decision is made when the aircraft is on the ground with full flaps extended, then set take-off flap before applying full throttle. If the aircraft has a retractable undercarriage (and unless the pilot's operating handbook states otherwise), then do not to raise the gear until the climb is well established and other more vital procedures can be completed — without distraction from the primary task of maintaining aircraft attitude and airspeed. There is always the possibility of the aircraft sinking to the surface if it is low when flaps are first raised, or mistakenly stowing all flap instead of raising the undercarriage. Pilots must be able to select and adjust flap positions, trim positions and undercarriage control without looking around the cockpit. At a public airfield, regulations require the aircraft to maintain runway heading until 500 feet agl. However, there may be a local convention that suggests aircraft track a climb-out path that follows safer terrain, in case of engine failure. Density altitude will severely deplete an aircraft's go-around performance. If high density altitude is combined with high gross weight and a short or uphill strip, then a go-around may be impossible. The reasons for a go-around from base or final approach might be: a perceived traffic conflict the landing area fouled an unstabilised approach or one that requires too many major changes in throttle setting an excessive sink rate on final, which may be evidence of downflow turbulence the approach is just too fast, too high or low, way off the landing line, or just confused. Go-arounds at or after touchdown are usually prompted by multiple bounces arising from a high rate of sink at first contact. Any time you have to pour on power to regain control of the aircraft, it is probably mandatory to then go around — provided there is sufficient remaining runway, there is a safe climb-out path ahead and the aircraft is not swinging. Many airstrips used by recreational light aircraft are just that — a strip lined by trees, scrub or soft sand. So, if the aircraft has swung away from the strip alignment, a go-around under those conditions may be unsafe. It may be preferable for you to make an early decision on the type of accident you may have by closing the throttle, establishing a reasonable aircraft attitude, holding tight and preparing for some relatively minor aircraft damage. It is better to hit the obstacles when groundborne rather than airborne; see 'Engine failure after take-off'. Here is an extract from an RA-Aus incident report: The pilot reported that ... "aircraft touched down in slow wheeler landing, bounced in semi-stall condition and yawed through 90 degrees. Full power applied, power lines were 140 metres away and line of 50 foot trees were 180 metres (away). Aircraft climbed at maximum angle of climb but neared the stall as trees got closer. Downwind component and high humidity didn't help the situation. Aircraft cleared the line of trees but then stalled and clipped a tree behind the first row of trees." In the preceding report you might perhaps substitute 'high density altitude' for 'high humidity'. The decision to go around must be executed positively as early as possible — don't be indecisive and don't start a half-hearted go-around attempt. Here is another extract from an RA-Aus incident report: "The pilot was practicing short landings and low power approaches. Just before the point of flare he decided to go around and applied power. After the aircraft had begun to gain altitude he decided to land ahead on the remaining runway. Again unhappy with the situation at the point of flare he decided to go around and reapplied power. At this point the left wing dropped and the aircraft slewed off the centreline and struck a sapling growing off to the side of the runway. The pilot was not injured but the aircraft suffered major damage." Elevator trim stall At each stage of the approach, the aircraft should be properly re-trimmed to maintain the desired airspeed at the current cg position and selected flap configuration. The elevator trim tabs exert quite a large control force at flight speeds. With full flap deflection on the approach, some aircraft may need quite an amount of nose-up trim; under these conditions, the application of full power following a go-around decision may induce a very strong nose-up movement — exacerbated by the elevator trim setting — and this attitude change must be anticipated by the pilot. If the pilot is slow in applying forward stick pressure and adjusting the elevator trim, the pitch-up may result in a highly dangerous 'elevator trim' stall. A similar situation may occur when conducting touch-and-go landings. On the other hand, if a lot of nose-down trim has been applied during the approach to landing, that also may cause difficulties on a subsequent go-around or touch-and-go if the pilot neglects to re-trim to the appropriate take-off setting. Read 'Running out of runway' in the July–August 2002 issue of 'Flight Safety Australia'. A go-around undertaken when the aircraft is low in energy has a much greater risk profile than a normal runway take-off, and thus must be conducted with considerable care. With the engine producing high power and the aircraft's attitude changing, the engine effects — propeller torque, gyroscopic precession and P-factor — will also be evident in a go-around. These effects must be anticipated and compensated for. Any turns conducted at a low energy level must be gentle and coordinated. See the safety brief 'Loss of control in low-level turns' and read this RA-Aus accident investigation report. 3.14.8 Short field techniques Planning for a short field landing is started with the airfield check in the flight planning stage. This is where the pilot ascertains airfield dimensions, slope, surface conditions, obstructions and hazards, plus forecast meteorological conditions. The next step is to calculate the aircraft's take-off distance under those conditions. If the calculations show ample margin for take-off, then landing — for a flap-equipped aircraft — should be okay, as it usually (but not always) requires a shorter distance for landing. It is best to do the complete landing distance calculation, factor in all the known conditions — but assume nil wind — then multiply that calculated distance by 1.5 to allow room for error. If the result is greater than the distance available, then landing at that field is unsafe. If the distance available is greater than 1.5 times but less than perhaps twice the calculated distance, then the approach and landing should be planned using short field landing techniques. The problem with airfields considered short for recreational light aircraft is that they are often poorly engineered, single, private strips and generally surrounded by obstructions. Some are built on rising ground, so that the landing can only be done uphill no matter what the wind velocity. Once committed into the final approach, the feasibility of going around is very doubtful. Do not plan to land at an airfield that is both short and one-way — it is venturing into the realm of gambling, not flying; and is most unlikely to be acceptable to the aircraft insurer. The following is an extract from an RA-Aus incident report: "The aircraft was being landed on a one-way strip with a tail wind. When it became apparent that the aircraft was not going to touch down in time, power was applied in an attempt to go around. The aircraft could not climb enough to clear some obstacles in its path so was turned to avoid them and, after clearing a shed, it struck a tree and came to rest. The pilot, who described himself as 'very, very lucky', was not injured even though the seat belt was torn from its mounting in the impact." It is not just the physical length of an airstrip that must be considered: under high density altitude conditions, many 'normal' airfields become 'short' and those same high density altitude conditions may preclude a go-around. Wire hazards Short airstrips seem to have an affinity for power cables to be strung across the runway ends — though I am aware of one private airstrip where the power supply to the house is strung across the middle of the runway, supported at each side by two poles. Remember, it is the wire the pilot didn't know was there — or knew was there but didn't see — that all too often brings an aircraft to grief. The following is an extract from an RA-Aus incident report: "The pilot departed his airstrip for one owned by a friend about eleven nautical miles away. Approaching from the west and about 1.5 nm from the threshold he began a gentle descent, passed over a set of power lines, then flew over a second set of lines, reducing his speed to 55 knots to set the aircraft up for landing. At this point he noticed the owner of the airstrip standing about halfway along the strip. The pilot, judging his approach to be OK, was contemplating whether he might need a slight application of power to flare on the uphill threshold when the aircraft struck a third set of power lines. The lines caught the propeller, exhaust and undercarriage, causing the aircraft to decelerate and strike the ground in a vertical attitude before coming to rest inverted. The pilot suffered minor bruising to the head and the aircraft was substantially damaged. The pilot involved supplied a list of 'points to ponder': 1. He had driven to the airstrip and inspected it from the ground three weeks previously. 2. He had previously landed on the airstrip from the east. 3. On the day before the accident he had overflown from the west in a different aircraft and then landed from the west. 4. The western end of the airstrip is in a localised low area and the poles carrying the power line were both obscured, one by a house and the other by trees." All of this indicates that pilots should be extremely wary of marginal airstrips and never carry a passenger into such situations. Perhaps many should be avoided, as they allow little margin to cope with micro-meteorological events that cannot be forecast — such as gusty crosswinds or lee downflows — and where a landing is really just a demonstration of pure bravado, perhaps with a dash of stupidity. Technique Getting into a short field requires accurate energy management (i.e. height and speed); firm, smooth controlling; and a properly calibrated ASI. You will have to choose a touchdown point that is closer to the threshold than normal, commence the flare a fraction later than normal and ensure the approach airspeed is slower than normal so that the approach angle is steeper than normal — particularly once clear of obstacles, and float is minimised by the aircraft being placed firmly on the surface soon after round-out. The steeper approach allows for obstacle clearance while still achieving the earlier touchdown, and also it keeps a little more potential energy of height in hand. If at any time you are not happy with the approach, then initiate an early go-around using the correct go-around technique. Be decisive — don't wait to see if you can recover the situation. Also, if you have made two missed approaches, then perhaps it's time to go elsewhere. Here is another extract from an RA-Aus incident report: "The pilot had made two downhill into-wind approaches to a short sloping strip but was unhappy with the speed of the aircraft and decided to approach downwind/uphill. As the aircraft touched down about 50 m along the strip he decided to go around and applied full power. The aircraft cleared a fence at the top end of the strip but then dropped a wing and landed heavily, collapsing the nosewheel and damaging the right main wheel. The pilot was not injured." Choosing a bug-out point and 'escape' route Short field landings require a little more preparation, starting with a slower initial overfly at 1500 feet agl and turn onto the upwind leg. During this period, find something that will clearly mark a point about halfway along the selected landing path. This will be the go-around point; i.e. if the aircraft has not touched down when it reaches this point, following the flare, then a go-around will be decisively initiated. You should be aware that an airstrip that is much smaller than those you are used to may prompt the tendency to scale down the circuit and the illusion that you are too low on final approach. See 'Runway illusions' in the March–April 2000 issue of 'Flight Safety Australia'. You must plan an escape route for the go-around from that bug-out point, and determine whether the aircraft will have the climb performance to clear any obstacles and high terrain on that route. Be aware that terrain slope discerned from 1500 feet agl is likely to be under-estimated. Also take into account that atmospheric conditions near the surface may not be what you expect. If you have any doubts — do not attempt a landing; that little voice telling you 'maybe this is not a good idea!' is understating the situation. You should plan not to touch down at the first pass, but to initiate a go-around before the flare and above obstruction height. This gives an opportunity to explore the final approach without any commitment to land. The low pass also provides a chance for a closer look for obstacles at the runway ends, a check of the surface condition and cross-slope, and to run off any wildlife. Landing routine 1. Follow the normal routine on the downwind leg, except fly it a little slower, lower partial flap and reduce to normal approach speed before commencing the descending turn onto base. This will provide more time to hold heading on base so as to carefully check for wind shear, which may further erode the safety margin between the reduced approach speed and Vso. If shear is indicated, a decision must be made whether to continue or to abandon the landing attempt. On base, reduce airspeed, lower full flap and keep the aiming point in sight. During the descending turn onto final, use a touch more power to balance the increase in induced drag and maintain the lower airspeed. Remember, during the approach, it is essential to re-trim the aircraft at the required airspeed after each flap and power change. 2. As early as possible after being established on final approach, reduce airspeed to the short field approach speed recommended in the Flight Manual. If that doesn't exist, use an airspeed that is at least 1.2 × Vso and a low power setting — you will tend to control airspeed with elevator and descent with power. The lower the power setting, the greater the sink rate. Remember, you will be flying the back of the power curve and the power setting used should be enough that there is ample reserve for a go-around if needed. Watch for apparent movement of the aiming point in the windscreen, and adjust power or airspeed to hold that point motionless. Also watch the top of the highest obstacle along the approach path. If the vertical distance in the windscreen between the top of the obstacle and the aiming point is widening, you should clear the obstacle; if it is narrowing you may not clear it. Start reducing the power when clear of obstacles. A suitably experienced pilot in a non-flap equipped aircraft can steepen the approach by sideslipping, but not with an inexperienced passenger as the manoeuvre can be a little frightening. 3. The slower approach speed means there is need to accurately maintain airspeed within 2 or 3 knots without continuous reference to the ASI, hence the need to accurately adjust trim. (All the foregoing presumes that the ASI accuracy, or variance from the stated Vso, has been calibrated). During the round-out, there will be a need to apply a slightly greater back pressure on the control column. This results in a consequent increase in wing loading and a further reduced margin between the accelerated stall speed and the airspeed, plus a greater tendency to balloon. Also, the possibility of an elevator trim stall following the application of full power, if a go-around is initiated, is more likely. Further reading The online version of CASA's magazine 'Flight Safety Australia' contains articles relating to landing that are recommended reading. Look under 'Take-off and landing' in the 'Further online reading' page. Signals that are essential to know When radio communication cannot be established by airfield control, there are five internationally recognised light signals that may be used to advise air and ground traffic at that airfield. A hand-held signalling lamp is used to direct the signal at an individual aircraft. The signals are a steady or a flashing green; a steady or a flashing red; and a flashing white light; as below: Light signals Directed at aircraft on the ground Directed at aircraft in flight Steady green — authorised to take-off if the pilot is satisfied that no collision risk exists Authorised to land if the pilot is satisfied that no collision risk exists Flashing green — authorised to taxi if the pilot is satisfied that no collision risk exists Return for landing Steady red — stop Give way to other aircraft Continue circling Flashing red — taxi clear of landing area in use Do not land Airfield unsafe Flashing white — return to starting point on airfield Before landing, it is essential to check the ground signal square usually located adjacent to the white primary windsock. The displayed ground signals denote the airfield operational state. Aerodrome is unserviceable, do not land. A cross or crosses displayed on a manoeuvring area denote unfitness for use. Aircraft operations are confined to hard surface runways, aprons and taxiways only. See AC 139-06 January 2011 'Use of restricted operation (dumb-bell) ground signals Gliding operations are in progress (and gliders have priority right of way) Wind direction indicators or windsocks Wind direction, variability and strength is usually assessed by observing the airfield windsocks — these indicate the direction and variability, and may provide some idea of the wind speed a few metres above the surface. Indication of wind speed will vary with the type of windsock. CASR Part 139, a Manual of Standards for Australian licensed aerodromes, requires one standard white windsock as the primary wind direction indicator located near the signal area, plus additional standard windsocks (yellow in colour) placed near runway thresholds. The standard cone dimensions are 3.65 m [12 feet] long, tapering in diameter from 900 mm [36 inches] at the opening to 250 mm [10 inches] at the exit. The standard light fabric sock indicates a speed of 15 knots or greater when it becomes horizontal in dry conditions, and about 7–8 knots when drooping at 45°. A wind speed above 2–3 knots is usually sufficient to provide a direction indication. Some windsocks may be colour-banded (red/white or orange/white) for higher visibility. Not all operators of aircraft landing areas comply with CASR Part 139, so a variety of wind direction indicators exist. They may be made from heavier materials; e.g. canvas, in lengths from 1.5 m to 7 m. Their positioning and condition range from useless to good. Wind speed indications may vary considerably from those of the standard. STRICT COPYRIGHT JOHN BRANDON AND RECREATIONAL FLYING (.com)
