Height/Altitude question.

[derekliston]

It was my understanding that :-Altitude is always height above mean sea level ie AMSL

 

Elevation is the height of terrain above sea level e.g an airfield's elevation or mountain's elevation

 

Height is the difference between altitude and elevation i.e. AGL

 

So given these definitions if the manual says you should state your altitude then it means AMSL, and if you are cruising above hilly terrain how the hell can you give an accurate height AGL? It varies every second.

 

Cheers,

 

Neil

Can't argue with any of that!

 

 

[facthunter]

Neil, yes holding a level when in hilly country is pretty secondary. LSALT has nothing to do with it , unless you are in IMC. (or MIGHT be). You need terrain clearance and manoeuvring room, and stay visual. If someone asked what level I'd say operating between 1800 and 2500 feet amsl (for example) or where appropriate remaining . OCTA etc Something which is useful to the enquiring pilot. Nev

 

 

[Jaba-who]

Can't argue with any of that!

Well, the whole point of my post was that you CAN argue with that ( despite the stupidity of doing it).

The rules DON'T say all those things.

 

They say partial things which do not, legally lead from one to the next.

 

The sensible person would accept they should but the wording of the rules do not.

 

That was my point.

 

 

[derekliston]

Well, the whole point of my post was that you CAN argue with that ( despite the stupidity of doing it).The rules DON'T say all those things.

They say partial things which do not, legally lead from one to the next.

 

The sensible person would accept they should but the wording of the rules do not.

 

That was my point.

Yes but my reply was to neil_

 

 

[408059]

I wasn't going to respond to this thread but facthunter has thrown up an issue that is relevant in my context. The airfields I operate from are between 2,700' and 3,600' AMSL with a lot of ground in between going higher. When I hear a radio call from the chopper and fixed wing boys calling heights AGL as they are visually inspecting power lines I understand why and it provides me with relevant information. In this context the form of communication is valuable.

 

 

[skippydiesel]

Somebody please explain this one to me. I fly from Warwick which has an elevation of 1536ft or thereabouts, therefore if I am flying 1000ft circuits I am at 2500ft. So why then do helicopters, army included make radio calls like "Departing Warwick tracking to Oakey, not above 500" Do they have different rules? because technically, at Warwick they would be 1,000ft below ground! I don't have a problem with it, I just want to understand why.

It seems to me the military do as they please and only abide by civilian rules when the mood takes them.

 

 

[ben87r]

Not above 500 is pretty standard heli call, basically saying they won't be high enough to bother anyone. Around here that may also become not above 1000 as well.

 

 

[poteroo]

This thread just points up the stupidity of some pilots. To use AGL is ridiculous unless you have an altimeter that can measure AGL. In places that I fly my AGL call would be incorrect, before I had been able to give it. The only way to get an accurate AGL is with radio altimetry and I have never seen an RAAus plane with that fitted.

In straight out non radio instrument informed VFR flight, it is difficult to really hold 500AGL. It's a lot easier to hold 200-250'AGL because even small 'hillocks' of maybe 100-200' will be obvious because they rise 'up' in the windscreen. So in low level survey, you can see these changes in elevation ahead of you and you can adjust power to hold your height AGL.

 

The main reason that aggies and LL survey/inspection pilots use the '500AGL' call is to reassure other traffic that they are in fact at 'low level' and should not present any conflict to other traffic. I've found that it's generally appreciated by higher traffic. I have flown surveys using RADALT and while it is effective - it's also seriously expensive. But, perhaps we are all overlooking the usefulness of stock, standard aviation GPS?

 

For years I have used GPS to help students, and myself, get our 'eye' in with regards to maintaining 500AGL. Remember that we have to teach some low level navigation in the Cross-country Endorsement. I have a Garmin Aera 500 in my current instructing machine and this is how it helps us.

 

1. set a user defined caution elevation. We set 500'

 

2. set a 90 or 120 second look ahead time

 

3. set the alert sensitivity to High.

 

The GPS is operating on satellite derived altitude converted to mean sea level based altitude. This altitude is only affected by satellite geometry - so if you have good numbers of satellites providing good 3D accuracy, then it's usable. Have a check of your QNH based altitude to the GPS altitude and you'll usually find they are not much different. The GPS-MSL altitude isn't subject to temperature or pressure variations.

 

So, to begin the exercise, we descend down to a height and watch for the yellow terrain alert to show as we reach 500AGL. We then increase power to fly just above where the alert shows yellow, and become more interested when the GPS screen shows more yellow ahead of us. It need not involve distracting the pilot from keeping eyes outside the aircraft because the switch on of the terrain page alert creates quite a flash of light. Pilot should become really alert if red is also on screen- but by that time the hill should have been visually acquired. You can setup the audio output to call '500ft' - which, can be/might be, useful when doing forced landing practice or even for circuit training.

 

By flying at on/about 500AGL as defined by the GPS database, the pilot can learn what everything looks/feels like. Knowing you are at 500AGL helps considerably in estimating distances, looking for landmarks, and estimating how far you can glide if the noise stops.

 

There is more to GPS than just pushing the GO/TO button.

 

happy days,

 

 

[Phil Perry]

Looking at Derek's original post. . . . it appears to me, as a bit of an 'Outsider' to Oz operations lately; that his comment was based upon fear of conflict after some Military bloke sent a fairly non descriptive and therefore useless and non-informative radio call, leading to confusion in the ear of the beholder and I agree with him wholeheartedly on this.

 

We have a different rule book in the UK, but the brass tack bits are quite straightforward in this particular instance.

 

When I want to inform the general flying public that I am either Approaching an airfield site with intention to land there, or Intending to overfly it en-route. In the Landing example, I call the station and say : FivePee Green Information, G-ABCD ( in phonetics of course ) Shedwing 912, one fife miles East, cruising 2,500 feet on the Birmingham QNH one zero one four, inbound, ETA wIth you at two zero, . request airfield information. . .

 

QNH . . .Q- Nautical height. = Reference to AMSL ie, my VERTICAL displacement above mean sea level, using a GIVEN reference, ie, Birmingham ( EGBB ) international airport. This ref was given to me by Brum ATC and I flew out of there using it in all their directional instructions to maintain separation from the RPTs and also outside of their airspace. THIS reference is ALWAYS referred to as ALTITUDE setting and NOT 'Height'. I would continue to use this reference until I decided that being clear of controlled airspace, and wished to continue flying in whatever direction,. . .

 

I would then call London Information for a regional Pressure setting ie RPS . . sometomes erroneously called AREA QNH' which is utter and complete Bollox as a QNH can only be specific to a particular station and all elevations are different ( unless you're talking about Holland ) There are 20 Altimeter setting regions in the UK, using the lowest forecast pressure in that region to provide adequate vertical separation for flights outside of controlled airspace. Hence pilots asking for 'The Regional' . . .I live in the 'Barnsley' region,. . although I am nowhere near Barnsley, the town bearing that name is is oop North somewhere in 'Coronation Street' country. . .! we even have Two of them which are all SEA areas, so that the RPS is exactly the same as the QNH, but . . well, that's the UK for you. . .! SKERRY is one,. . I can't recall the other one. . .

 

This is all most useful, as it means that any outgoing, or other incoming traffic on FivePee's frequency are immediately aware of my general location at that time, and direction of intended travel at THAT PARTICULAR 'ALTITUDE' reference.

 

The more 'Switched On' persons monitoring the channel, would know that my 'SHEDWING 912' is only capable of 77 and a half Knots, so they could mentally extrapolate from this, that they could easily 'Beat' me into the circuit at FivePee by around five minutes and thereby get to the Fuel Bay, or the Restaurant, or the Bog, a little faster than I could. . . .

 

The destination airfield then give me their current QFE based upon the elevation of the field above sea level, on that particular reported pressure setting. ( Q - Field Elevation ) so that my arrival in their overhead is the same as indicated on my altimeter but this time in AGL TERMS. . . as others in circuit, or those departing that site,. . . and we are all singing from the same hymn sheet.. OK No difficulty with that. . .it works very well.

 

If some donkey in a Heelo ( Sorry HIC, no offence intended ! ) calls on the radio and says. . .. "I'm going to overfly your site at 500 feet AGL" . . .He / she would get rapid short shrift and told to pull in His / Her head. The military hereabouts just DO NOT DO THIS. They are VERY KIND to 'Leisure Flyers' . . . hence their lack of reluctance to allow us to land at any of their bases without exception, and charge us ZERO fees for the privilege of dining in their taxpayer funded eateries. . .( ! )

 

It Wasn't really a can of worms that you opened Derek, . . .but that is what this site is all about. I find it most interesting to read about how things work in Australia nowadays. . ., since I left in late 1982. . . .!

 

 

[frank marriott]

sometomes erroneously called AREA QNH' which is utter and complete Bollox as a QNH can only be specific to a particular station

Not quite correct Phil (for Aus anyway). The area QNH is declared (call it an average) for a specified area in order that all traffic in that area will be using the same reference base for separation - some nearly the size of England. Interestingly enough no change to when you were operating here in 82.

 

 

[Phil Perry]

Not quite correct Phil (for Aus anyway). The area QNH is declared (call it an average) for a specified area in order that all traffic in that area will be using the same reference base for separation - some nearly the size of England. Interestingly enough no change to when you were operating here in 82.

Frank,. . .as I said in my post, AREA QNH just can't work in a country the size of the UK. Yes,I REMEMBER IT, from my flying time in Aus. This is why the UK adopted the REGIONAL PRESSURE SETTING system. Which works very well. To illustrate this a little, a local man, who owned a Butcher's shop in Shropshire, owned a nice Mooney aircraft. One day, he flew out of Sleap airfield in Shropshire, taking a random passenger with him, and flew down South to an airfield called White Waltham, not far from London, and beneath the Heathrow control zone.

 

They had lunch,. . had a bit of a look around at all the vintage aircraft owned by the local London millionaires, and then proceeded to fly back to Sleap in the mid afternoon. The WX forecast was badly wrong,. ( what a surprise. . . / sarc. ) and a cold front was moving over the British Isles from the North West.

 

The last message received from the aircraft was that it was flying overhead Halfpenny Green Airfield, ( 20 NM from home base ) at 1,600 feet in IMC. . . the Pilot was the current holder of an IMC certificate. . . .

 

Shortly thereafter,. . .radio contact with the aircraft was lost, and witnesses said later that they heard a sort of 'banging crunch' sound in the foggy conditons around the Wrekin,. . the only piece of high ground for many miles in any direction, this being a long extinct volcano of some 1500 feet elevation. . . .

 

For some reason, the pilot had not accounted for the fact that he was flying rather quickly into an area of rapidly reducing atmospheric pressure,. . .thereby causing his altimeter to over-read the actual level at which he was flying in real terms. . .ie, he was unwittingly flying DOWNHILL. . . .. Halfpenny Green Information gave him their current QNH, but after the examination of the wreckage the AAIB said that he had not changed the altimeter reference to reflect this information .. . . his aircraft struck a near vertical rock face called 'The Eagle's Eye'. . .just 50 feet below the summit of the hill,. . whilst travelling at circa 185 Knots.

 

THIS is ONE of the reasons that why we use REGIONAL pressure settings for VFR flight outside of controlled airspace in the UK. . . . the pressure changes far too rapidly to use an 'AREA QNH. . .)

 

One Millibar of pressure = 30 feet of height displacement ( The bloody Europeans now insist that we drop Millibars, and use 'HECTOPASCALS' this measurement is identical to the Millibar, and even the beloved BBC, have ignored this edict completely in their shipping reports at 6 AM and midnight. . . On;y thing they've ever done which makes any sense. . .! )

 

However,. . .I don't have an argument with your 'Area QNH argument. . ., as Australia is mightily larger than the British Isles mate. . . . .

 

 

[peter2480]

Who the hell wants to be above 500' AGL anyway. Way too cold!!

 

 

[ben87r]

In AUS not accountanting for altimeter error we've 45 hectobars/millipascals of terrain clearance minimum en-route so although not changing the altimeter setting would be an error it would take an extreme example to bump into Mother Earth.

 

Phil do you mind educating us on the difference between area and RPS?

 

 

[peter2480]

In AUS not accountanting for altimeter error we've 45 hectobars/millipascals of terrain clearance minimum en-route so although not changing the altimeter setting would be an error it would take an extreme example to bump into Mother Earth.Phil do you mind educating us on the difference between area and RPS?[/quote

Not sure what you mean by terrain clearance here - your quoted 45 millibars sounds like minimum LSALT for IFR. Terrain clearance VFR is 500 ft above terrain or 1000 ft over built up area. Accidents are a chain of errors - although 45 millibars is 1350 feet, attention to accuracy maximises the buffer between error and happy days. Keep in mind that there are other obstacles out there too - other aircraft need to be sure of your altitude for effective separation.

[Phil Perry]

Not quite correct Phil (for Aus anyway). The area QNH is declared (call it an average) for a specified area in order that all traffic in that area will be using the same reference base for separation - some nearly the size of England. Interestingly enough no change to when you were operating here in 82.

Clumsy post again Frank, sorry. I should have added that the REGIONAL PRESSURE SETTING is also 'DECLARED' The settings, whilst not arbitrary, are CALCULATED are based upon long term monthly means ( 'Means' equating to 'Mean averages' in case of confusion here ) combined with the Lowest forecast pressure for that region on the day. In the UK, the LOWEST level which can be used as a Flight Level, using the international standard ref 1013.25 mB / hPa, is FL35. But this level can only be used for flight planning if the forecast pressure within that region will not create a ground clearance issue.

 

Since Ben Nevis in Scotland is 4,409 feet elevation, and Mount Snowden in Wales is 3,560 ft, you could not use FL35 if your flight transited anywhere either of these bits of ground. . . in reality, I do not know anyone who has ever planned a flight in the UK below FL45, but that's anecdotal. If you want to go mountain flying in VMC, then most pilots would simply use the Regional setting whilst outside of controlled airspace. . .Flight levels are for RPT and or IFR ops AFAIAK. . . .( But if you don't like this opinion, . . .I DO have others )

 

I have not seen a general Nav chart covering large 'ish sections of Australian states for rather a long time. . so I do not know if the charts are divided into graticule squares having a large and a small number in the top left corner indicating MEF. These are Maximum Elevation Figures, so that a number 2, followed by a smaller number 4, would indicate that the highest elevation within that graticule was 2 thousand four hundred feet. NOW this means terra firma. It does not indicate a 1500 feet high radio mast on top of a 2 thousand feet high ridge. . .so these are only a general guide. ( I must point out here that I am currrently referring to the 1:500,00 scale Nav charts, as supplied here in the UK. )

 

The MEFs are there to attract the pilot's attention initially, so that she / he can check her / his intended track against various elevations and look up any TV masts shown thereon. . .

 

One other thing, from memory the 'Transition Altitude, above which all reports regarding the vertical displacement of your aircraft should be reported in Flight Levels is, or Was 11,000 feet in Australia. In the UK it's still 3,500 feet, with the slight difference that you MAY use QNH and fly quadrantal heights if you wish, and do not have to use Flight Levels if you do not wish to.

 

One Other, Other thing Frank ( ! ) I DO rmember in the dusty recesses of what uesd to be a brain, that I was flying on Area QNH on a flight from Casey Airfield, Berwick, to Jeriderie and then to Nhill via quick visit to collect another ne'er do well friend at Mildura. . . On the Mildura to Nhill leg, mate Gerry in the Right seat, screamed LOOK OUT !!!! . . #'F#CK*#'@* . . .just then,. . a twin aircraft passed across in front of us from right to left VERY Bloody close indeed. . .I DO know that I was flying the correct quadrantal for the heading, and we were above 8,000 feet. . 'ish. . I had to do it properly with 3 other pilots on board ! ! ! ! !

 

Memory is now fading but it was only around fifty metres OR LESS. . .we were flying VH-IWK , a C-210 borrowed from Keith at Berwick, and cruising at 142 Kt TAS. . . .I had no time whatsoever to react, other than to turn and get a quick rear end view of him disappearing into the distance. Gerry reckoned it was a Piper Aztec,. . .?? Must've had brilliant eyes then, all I could tell from behind was that it was a low wing twin. . .

 

I reported this when we got back to Berwick, but was advised not to open Pandora's box, unless I really wanted to enter into a paper swapping competition with DCA for a few months just because some poor bloke got his quadrantal wrong . ..maybe his Missis was on board nagging 'im ? ?

 

 

[frank marriott]

Not that it makes a lot of difference Phil but you may be interested to know that one change from the 82 times we have changed from the quadrantal levels to hemispherical levels in Aus.

 

 

[Phil Perry]

Thanks Frank. . . If I can ever afford a trip to Australia, SNF pass a GA medical ( ! ) that will be very useful info,. . .providing every other bugger uses it properly just like they Don't bother doing up here ( /sarc ) strange,. . .I always thought that using Quadrantals was one of the better, more sensible ideas for 500 feet of separation BUT, Obviously, greater minds than ours have prevailed. . .

 

I really Liked the 'Quad' rule. . .made sense. . . North to 089 ODD,. . . East to 179 ODD +500,. . South to 269 Even,. . . West to 359 Deg, Even + 500. . .what was wrong with that ?. . . .If it ain't bloody well broke,. . .why fix it I wonder ?. . or was it too difficult for these poor Newbies to grasp you think ? . . . flying cars for the public ? ? ? HAHAHAHAHAHAHAHAHA. . . oh dear, my sides hurt. . .we can't even organise the damn sky for people who are Good at using it . . .it would seem. . . .!