What happens when the engine or propeller fails in the initial climb?

[Admin]

Recreational light aircraft engine/propeller failures in flight are not rare and generally are not particularly stressful except when failure occurs in take-off or go-around mode. The take-off sequence in a light aircraft is the most critical of all normal flight procedures; all the engine's available performance must be employed during the acceleration and initial climb, leaving no power in reserve. Also there is no potential energy of excess height or excess speed available so, during take-off, the pilot's options are very limited — even more so in high density altitude conditions. All recreational light aircraft are low-inertia aircraft — the 'draggy' ones are low-inertia plus low-momentum aircraft — so are detrimentally affected by rough air at low levels.

 

If complete or partial loss of thrust occurs shortly after lift-off, the best and probably only option is to promptly establish a safe descent attitude and speed, and land on the remaining airstrip, ground looping if necessary to avoid an obstruction. It is only if total loss of thrust occurs after achieving a 'decision height' that a safer option other than land more or less ahead MAY exist. A possibility of loss of control is introduced any time that loss of thrust is experienced in the climb or in a turn.

 

There is a strong compulsion to minimise airframe damage — very understandable if the aircraft has taken a long time to build or acquire — but the overriding priority has to be 'save your skins and sod the aircraft'.

 

This module presumes the reader is familiar with the contents of the earlier 'Don't stall and spin in from a turn' and 'Don't land too fast in an emergency' modules, which are pertinent to this document.

 

4.1 What happens when the engine or propeller fails in the initial climb?

 

A recreational light aircraft established in the climb attitude at Vy (best rate of climb speed) has an aoa perhaps around 6–8°. At such angles there is significant induced drag so when thrust is lost, for any of a multitude of reasons, the aircraft may rapidly decelerate to stall speed — worse if the airframe also has much parasitic drag. The immediate action required is to convert the potential energy of height to a safer speed. When climbing at Vx (best angle or emergency climb speed) aoa could be around 8–12°, so deceleration following power loss is a greater hazard. Of course recreational light aircraft Pilot Certificate holders are aware of this and take immediate action to lower the nose to a position consistent with their estimate of the approach or glide attitude in pitch. Or do they?

 

Pilot and aircraft reaction times

 

Material developed by the late Mike Valentine, the former RA-Aus Operations Manager and prestigious GFA stalwart, is included in this section. Mike conducted considerable research into pilot and aircraft reaction times following cable breaks in winched glider launches and engine failure after take-off in recreational light aircraft. Some research results — which were very similar for both aircraft categories — were published in the June 2004 issue of the RA-Aus journal, and are summarised as follows.

 

• Following an engine/propeller failure in the climb, there is an initial delay while the pilot's brain adjusts to the shock of the event and then she/he pushes the control column forward. This reaction time appears to average around three to five seconds, much longer than might be imagined, but similar results are obtained in tests by other aviation bodies. Mental paralysis/disbelief, i.e. 'this can't be happening?', is the main contributor to that delayed reaction; meanwhile the aircraft is slowing at perhaps 2 to 4 knots per second. It can be exacerbated by slight panic if the power loss is accompanied by very unusual engine noises, smoke and/or violent shaking.
   
   
  
• A quiet breakdown in the propeller speed reduction unit results in the unloaded engine's rpm increasing while the propeller is 'freewheeling' — producing no thrust — and it may take a little longer for the pilot to realise what has happened.
   
   
  
• If the aircraft is equipped with an effective elevator trim system and the pilot has trimmed for the climb speed — which is generally similar to the best glide speed — then the aircraft will of course try to regain its trimmed speed when thrust decreases; however, this takes too long to stabilise, and the pilot must take firm control and push the stick forward.
   
   
  
• As the pilot pushes over into the glide attitude the aircraft follows a curved flight path. During this manoeuvre, pitch attitude and wing loading are changing, and the aircraft still slows for two or three seconds before accelerating. When the desired attitude is eventually attained, the pushover is terminated and the aircraft is then apparently stable in its glide attitude.
   
   
  
• Apparently? Yes because, although the aircraft is in the required nose low attitude, it has just been through an energy-changing manoeuvre without the benefit of thrust to sustain it. Its inertia, aided and abetted by its drag, prevents it from immediately attaining the airspeed appropriate to the glide attitude; some seconds must be allowed for the aircraft to build to that speed. Gravity alone can't instantly accelerate an aircraft to a safe speed through a 10 or 15 degree pitch attitude change.
   
   
  
• The real EFATO event will be noticeably different from that experienced in a simulated EFATO because there is no residual thrust from an idling engine. If the propeller is windmilling there will be additional drag and thus a bit steeper descent path. Also the lack of a cohesive propeller slipstream over the tailplane will make the elevators feel different — and less effective.
   
   
  
• Any attempt to start manoeuvring the aircraft without allowing sufficient time for the indicated airspeed to build to, and stabilise at, a safe speed will risk loss of control — and don't think there is a discernible lag in the ASI; there isn't if it is in good condition and the pitot-static system is unobstructed. If the pilot lowers the nose to the glide attitude and immediately performs just a moderate 'bank and yank'manoeuvre, the aircraft may stall and spin. At least five seconds will elapse from the moment the pilot pushes the stick forward to the time the airspeed margin over stall is safe enough to carry out a gentle manoeuvre. The diagram below represents the result of Mike's tests in a simulated (and placid) EFATO when climbing at 55 knots (about 1.3 Vs of 42 knots). Similar results were found in other tests. The diagram doesn't show the 3–5 seconds reaction time for the average pilot, as the pilot for the test series was conditioned to an expectation of the throttle being pulled by the observer.
  
  

  
   
   
   
  

• During the pushover, the control column was pushed forward smartly enough and far enough to unload the wings to perhaps 0.5g or less, so that the aircraft is still totally controllable even if the airspeed reduces below the normal Vs1 of 42 knots. At 0.5g the airspeed will build relatively quickly because the lift will be nearer zero and thus induced drag is reduced to nearer zero.
   
   
  

 

 

Unloading the wings is a good practice to practise

 

As mentioned in the flight envelope section of the 'Don't fly real fast' article a light aircraft can be safely held at sub-Vs speeds for several seconds by unloading the wings so that the aircraft is operating in the reduced-g band between zero g and +1g, but not in negative g. The stall speed between +1g and 0g is still proportional to the square root of the wing loading g ratio, as indicated in Table 4.1.

 

 

 

 

 

Note: when the wings are unloaded, ailerons and rudder can be used in ways that would be regarded as excessive at 1g loads. This unloading technique also has value as a stall recovery exercise (at a safe height) for pilots to really comprehend what is going on. It involves unloading the wings to perhaps 0.25g by pushing sufficiently forward on the control column so that you feel very light in the seat but not yet constrained in the harness as you would be if imposing negative g — or if dirt and dust start floating up from the floor. When unloaded — which takes an instant — roll the wings level (holding near zero g of course) using full aileron and whatever rudder is necessary (often a boot full), and centre the aileron and rudder as soon as the wings are level. As drag at that minimum aoa is much reduced, speed will build more quickly and thus dive recovery is started earlier. With practice, the total height loss by taking such decisive action may be less than in a gentle reaction, and the speed will stay well within the allowable envelope in most recreational light aircraft. There will not be any fuel system problems as long as negative g is not applied. However, if forward pressure is slightly relaxed and the aircraft allowed to return to its normal 1g state while airspeed is below Vs1, the wing will promptly stall.

 

 

[P4D]

"Recreational light aircraft engine/propeller failures in flight are not rare <snip>."

 

Are there any statistics to back this statement? My observations is this is not an accurate statement.

 

 

[Sapphire]

I read some where a while back that RA and GA aircraft have similar accident rates. This does not mean they have similar engine failure rates. A lot of ultralights can sneak into a small landing space at a lower speed. If there is any impact damage, it is significantly reduced. Half the speed equals four times less impact force. That 'shock period" of several seconds can be addressed with preparation. As you climb out [every time] in addition to evaluating landing options you are training an automatic push the stick forward reflex. Don't sit there like a stunned mullet. Do it if the engine fails. Every time I do sharp manoevers for fun or any other situation, the stick is pushed forward, without thinking, if only to compensated for the extra drag. Flying involves feeling what the plane is feeling.

 

 

[facthunter]

I don't disagree with anything written there. The part written in italics ( the last bit) should be fully understood because it enables you to maintain control and manoeuver at stall and below speeds. The instinct is to pull back on the stick and the opposite is required sometimes. Nev

 

 

[poteroo]

Right on, Nev.

 

If you have done your preparation for take-off properly - you will have already made a 'decision' as to whether you'll need to turn L or R, or go straight ahead off the strip in use. That's a given for any t/o, but particularly in the bush. Instructors - don't allow your student to make any take-off without them doing this exercise. If the pre-EFATO decision was to make a turn - then if you unload the wing quickly, and continue this for a few secs - it's possible to make a substantial turn towards a safe landing spot. Keeping the nose down, despite a windscreen full of scenery, is the only way you get a turn out of the EFATO.

 

happy days,