Altitude / height questions - help !!

[Teroc]

Hi folks,
How do you guys teach your students to tackle QNH/QFE/QNE questions ?
I know all the individual breakdowns..ie 1mb=30 ft.. high to low watch out below etc etc but when im presented with a question like the one below i find myself tearing my hair out trying to "Juggle" the figures.
Is there a simple equation / formula or memory aide which helps ? Should i work out everything in QNH and then convert to QFE / QNE ?
Any help greatly appreciated as im doing the PPL tech exams this friday..arrghh !!!
Teroc
Heres the question folks..you know the type :)
"A plane leaves an aerodrome "A" which is 500' above sea level with a qnh of 990 mb and flies to another aerodrome "B" which is 200 ft above sea level with a QNH Of 1010. Assuming the pilot doesnt recalibrate altimeter from QNH at aerodrome "A" and maintains a height of 500 feet after leaving aerodrome "A" what is his actual height above runway level of airport B ? Whats his height above mean sea lever ?

[Snigs]

High to low, down you go

If QNH (read pressure) goes down then the altimeter will read higher than you actually are (i.e you go down).

In this case, (if my brain is in gear), your altitude at A is 1000'. The altimeter will still read 1000' at B (no sub-scale change). The actual altitude at B is 600' ((1010-990)*30) greater (pressure rise) , = 1600' Thus your height above the runway is 1400' (altitude less the difference between sea level and runway elevation).

Confused? Well I am.

----------------------
Snigs
God help me if I'm wrong!

[Squealing Pig]

I get the same results as Snigs

I thought about it this way.
just break it down into logical steps.

When you get to B ask yourself :-
Where is the 990 Mb layer if the 1010 layer is at sea level?

990mb is lower than 1010 so the layer has to be above

1010 - 990 = 20mb 20 * 30ft = 600ft

so 990mb layer is at 600ft above sea level

your altimeter shows 1000ft with reference to 990mb, so that is 1000ft above the 990mb layer

1000 + 600 = 1600ft above sea level and 1400ft above airfield B.

Well if two of us get it the same it must be right!

P.S. When I did the exams at ATPL level I was advised to use 27mb / ft unless told otherwise in the question.


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Push forward - Pigs get bigger
Pull back - Pigs get smaller
Pull back some more - Pigs get bigger again

[GT]

This may not be of very much use if you're trying to fly an aeroplane at the same time, but I always found drawing a diagram helped with these problems.

[Charlie Foxtrot India]

Diagrams are good, a picture tells a thousand words. Just ask Saint Trevor Thom.

Also a variation on Snigs' theme:
"High to low, beware below" Applies to temperature also.
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[This message has been edited by Charlie Foxtrot India (edited 08 September 1999).]

[BEagle]

Squealing Pig, GT and Charlie Foxtrot India are absolutely right - draw a quick diagram and NB where the various 'pressure levels' are.
PS - Best of luck with the PPL exams, Teroc!! And you'll get a debrief to find out and correct whatever you got wrong. Which is more than you do with the 'tick and forget' commercial exams in the UK!!

[This message has been edited by BEagle (edited 08 September 1999).]

[Teroc]

Thanks for the good luck Beagle regarding the exams..i'll let you know how i got on..
All,
Thanks for the help above..
A diagram does make things a lot simpler.

Teroc

[BEagle]

Teroc - how did the exams go? Which set did you sit?

[Teroc]

Hi Beagle,
The exams went ok thanks..I did the lot as its my first time doing them.
Aircraft general, aviation law, human factors, flight performance and planning.
I thought some of the questions in the flight performance and planning were really unfair.
In some of the find the Heading/groundspeed type questions the answers were within 2° of each other...as we all know the crp 1 has a certain degree of error when calculating these and it wasnt taken into account. I did one problem 4 times and got 4 different answers each time all within 1 degree of
201° each side...the answers you could pick from were the usual 2 ridiculous ones and also either 200° or 202°.
I felt 2 degrees error when working out manual flight computer probs was a bit tough...there were a couple of eta/conversion questions which also didnt account for the error of the computer... If a human marks them thats ok because they will see you were fairly close but as far as i know a computer optically scans them for answers.
The human performance was a joke...16 questions in 30 minutes...everyone had them done in 10 !!..really easy....felt a bit cheated that i'd paid £20 for Trevor thoms book and got asked stuff my mother would know :)
Law had a lot of JAR stuff which threw me a bit and aircraft general was fairly good..hard but fair...A long day though....

I'll know if about 2 weeks so fingers crossed :)

Teroc

[BEagle]

Teroc - your PPL exams should have been marked by an authorised Examiner!! They are certainly not marked by a computer and the answers do allow for a degree of leeway. The whole idea of the PPL exam marking is that you shall be DEBRIEFED on your errors if you pass so that you will learn from your mistakes!! If you fail, you should be given some general advice on areas which require more study. But to do all the exams in one go is quite an effort - I hope that you weren't too knackered at the end of the day. I hope that you get a good result!! If you fail them, I really recommend getting hold of the AFE 'JAR supplement' textbook before you sit them again.

[Teroc]

Thanks Beagle,
Actually i was wrong earlier. I found this out this morning. The exams are marked by an examiner..sorry about that.
Thanks for the book tip...i'll certainly give it a look..even if i do pass...i dont think you can ever learn enough.....
I'll know in about 8 days apparently...fingers crossed...
Teroc

[Teroc]

Beagle and pals.....
Got my results on friday....
passed everything except air law which i missed by a measly 1 %... i got 69% and the pass is 70%...arrghh :)
So it looks like ive got to re-sit Law in October....
Still though i dont really mind doin that..i was a bit unsure about the law one as there was a lot of new JAR stuff which threw me...
at least i passed all the "Stick and rudder" type exams which i was happy about...

Thanks to you and all the Ppruners who helped me along the way..cheers folks..

Teroc

[BEagle]

Good to hear that you passed most of the exams - well done!! Once you've had a couple of celebratory beers, treat yourself to that AFE 'JAR Supplement' and you shouldn't have too much trouble next time.
Ken at the CAA knows that the Air Law exam is rather poorly served by text books at the moment - but your examiner should now have given you some general guidance as to the main areas you need to work on. Good luck with the re-sit!!

[Teroc]

Thanks Beagle....had a "couple" of beers to celebrate on friday night..urrghhh :)
Im actually in Ireland so im not sure if the AFE JAR supplement will cover Irish law....i'd imagine it would....
The IAA arent much help either with regard to the latest JAR stuff unfortunately but sure we'll give it a go eh?...at least i can dedicate all my study to one area for the next exam..
Cheers again...
Teroc,
By the way Beagle whats your background in aviation..instructor / pilot ?

[BEagle]

Not sure how the authorities in Ireland compare with those in the UK re JARs - the AFE supplement is geared towards the extra bits you would need to look at for the UK JAR PPL compared with its CAA predecessor!!
My own aviation background? Well - although my past flight envelope was up to 50 000 ft plus and beyond Mach 1.lots, my current day job as a jet training captain pays the bills, but in my spare time I'm also a PPL instructor and examiner.

[Teroc]

Wow Beagle im impressed..
Fairly good CV i reckon :)

Thanks for all your help over the past few weeks ..it really is appreciated..
Perhaps some day i'll be doing a line test with you, go easy on me :)

Teroc

[BEagle]

Kind of you to say that, Teroc. Enjoy yourself in the USA - if you've kissed the Blarney, you'll find the locals will enjoy your visit as well - particularly the ladies!! You might be surprised at the quality of 'instruction' you get - but your basic training will stand you in good stead!! And best of luck (with Aer Lingus ?) in the future!!

[Teroc]

Haa haa...nice one Beagle :)
I'll let you know all about that "Circuit" and my "touch and go's" as well when i get back :)
Tried the Aer lingus cadetship route this time around but unfortunately didnt get very far... will keep plugging away though..if anything it made me more determined to get there in the end..
Thanks again
Teroc

[MEL]

Try and figure this out !

Aerodrome 1:
Madang (AYMD) Elevation 11 ft AMSL
05 12 33S 145 47 15E Temp 31 C QNH 1008

Aerodrome 2:
Mount Hagen (AYMH) Elevation 5350 ft AMSL
05 50 00S 144 18 00E Temp 23 C QNH 1024

Both airfields, if you plotted them are in the "doldrums" of the ETZ therefore should have low QNH's.

The question is:
Why is the station QNH so different considing less than 100 nm seperate them ?

The answer will be posted in several weeks.

[Checkboard]

You want the answer here?

Hint: look at the elevations.....

[MEL]

Why not let the uninitiated have a go -

Hint: Other airfields of similar elevation work quite well on an area QNH of 1008

[Squealing Pig]

MEL, Has this got anything to do with the fact that QNH is being used rather than QFF ?

Just a thought !

SP