Altimetry problems and solutions.

[trafficwas2]

Hi all,
Just wondering if anyone has a few (or many) altimetry problems with answers for practice?
At the college and wanting to keep on top of study etc.
thanks in advance.
traffic was.:}

[Glamdring]

There are 2 main formats for altimetry questions at the college....

Format 1...

QNH = 997mb
Transition Altitude = 6000'

State the lowest flight level (transition Level) and the thickness of the transition layer.

Change the QNH as many times as you like to change the question.

Format 2...

Danger area to 7500'
QNH = 1002mb
Transition Altitude = 3000'

What's the lowest flight level available to overfly the danger area and how high above it are you.

Again change the Height of the danger area and the QNH to change the question.

[2 sheds]

...and explain in your own words the significance of the QFE in the above! Not to mention the evident confusion between TL and TA. Should have thoroughly confused the poor guy.

2 s

[stu_h]

Another favourite for oral boards is:

A/c A is at (eg) FL70
A/c B is at altitude (eg) 6000 on a QNH of 972

How many feet (or not) are they separated by.

Change figures to suit, and watch out for the ones where they arent separated at all :)

[ZOOKER]

QNH at EGLL 1005mb.
QNH at EGQL 991mb.
What is the most likely frequency of the ILS in use at EGGP?

[goatface]

QNH at EGLL 1005mb.
QNH at EGQL 991mb.
What is the most likely frequency of the ILS in use at EGGP?

25 metres and 32 Deg C. Totally bleedin obvious innit?:rolleyes:

[ZOOKER]

goatface,
wrong! VHF Radio frequencies are usually measured in Megahertz (MHz). :E

[Glamdring]

Yeah, sorry. My questions should say "Transition Altitude" and not level :ok:

I've edited it now.

[wings folded]

wrong! Radio frequencies are usually measured in Megahertz (MHz).


No, only some frequencies are measured in MHz.

There are also Gigahertz, Kilohertz and even Hertz all alone, but you need to be a whale or a submarine to receive the latter

[ZOOKER]

You are on a VFR cross-country flight from EGMD, (QNH 1029mb) to EGPG (QNH 1015mb).
Due to the persistent ache in your left ankle (which has been counteracting the en-route drift) you forget to reset your altimeter.
On arrival at PG will your altimeter,
a). Under-read.
b). Over-read.
c). By how much?

[ZOOKER]

Good spot Norwich, - and don't forget Terahertz radiation! :ok:

[HEATHROW DIRECTOR]

trafficwas2.. Firstly, please excuse the idiots on here. I'm afraid we're stuck with them.... but some of us try to help.

Here's a good tip. With altimetry questions keep this in mind: When you increase the sub-scale reading, the altitude reading increases. When you decrease the sub-scale reading, the altitude reading decreases. Just keep that in mind and I hope it helps you. I was told that by an instructor 45 years ago and never had a problem with altimetry questions since..

Good luck..

[wings folded]

I don't know if HD had me in mind as one of the idiots we are stuck with, but even so, on a serious note, I offer a slight variant of his advice.

Remember that as you climb, pressure decreases. So if your altimeter stays at the same subscale and you are heading towards lower pressure, and you maintain a given height according to your altimeter ( say, 2000 feet,) you may think you are at 2000, but you may in fact be a lot lower. (About 28 feet per millibar, if I recall correctly)

It is the same principle HD speaks of, but looked at in a slightly different way.

Different folk are receptive to different ways of looking at things. So this way of looking at it might appeal more to your logic, or maybe not, but I hope it helps.

[2 sheds]

The significance of the QFE is that the danger area is based on height above the surface. You would either be given the QFE or the QNH and the height of the surface above MSL.

This is still making no sense!

http://static.pprune.org/images/statusicon/user_online.gif http://static.pprune.org/images/buttons/reply_small.gif (http://www.pprune.org/newreply.php?do=newreply&p=4955535&noquote=1)

[Sideshow_90]

2 sheds -
If you use QFE, you get the height above aerodrome, therefore above the surface.
If you use QNH get altitude above mean sea level, so if using then must know danger zone limits based on mean sea level...

I think?

[ZOOKER]

Where is 'Flight Level Zero'?
Name at least one ICAO EUR Region airfield where the QNH is less than the QFE?
During a normal display routine, what correction must a 'Red Arrows' pilot apply to a pressure altimeter to enable it to read accurately during the time spent flying inverted?
What altimeter setting would you use if 'climbing straight ahead on runway heading'? :E

[Ivor_Novello]

Aaarghh..

QFE and Danger Areas usually don't go together well !!!
If you use QFE, you get the height above aerodrome, therefore above the surface.
Aerodrome ? Surface ? There's a lot of different surfaces around the Aerodrome... which one ??

QFE is used by pilots who can't add 1000 to the airfield elevation to fly a visual circuit. For everything else there's Mastercard.. er.. QNH !!!

I suggest to whoever was looking for altimetry questions, to stay away from this thread and to Glamdring to stay off the glue :) I think I'll avoid flying to your airport when the pressure's low ;)

[ZOOKER]

trafficwas,
Surely the original thread title should be:-
'Altimetry challenges and solutions'. :}

[Glamdring]

I've changed the QFE to QNH. (I was tired when I wrote those questions :})

Here's a problem involving QFE...

ATZ from SFC-2000'
Aerodrome elevation 326'
QFE - 985mb

What's the QNH and at what altitude do you need to overfly the aerodrome to stay clear of the ATZ?

[PDF]

To the OP,

I can't help with your problems but I suggest you use the Ignore function for some people, the more you check around here the more you'll get the idea who to listen to and who to not..

Wings folded, don't think HD was referring to you!

[ZOOKER]

trafficwas2,
An American pilot requests the QNH in inches.
Where would you find it?

The barometer at your airfield is rendered u/s.
How could you determine QNH and QFE?

[ZOOKER]

Why isn't QNE used in the UK?
What is QFF?
Explain the significance of the names adopted for the UK Altimeter Setting Regions?
Have you ever been to Barnsley? :E

[anotherthing]

who says QNE is not used in the UK...

[NBanker]

who says QNE is not used in the UK..
Well, I guess there's nothing to stop anyone using it if they really wanted to but with the UK's highest airfield - Rossendale - being only 990ft amsl there just isn't any need for it. Unless it was the most incredibly low pressure at the time, it would be well within the range of a standard altimeter's subscale.
NB

[Glamdring]

I see your Rossendale and raise you Treborough at 1200ft amsl. :ok:

[anotherthing]

NBanker

I think in some aircraft (very old ones) QNE was used if the pressure was less than 950Mb (I think that was the figure - never had to use it myself - I'm not that old!). Newer Altimeters can handle this. There are still some old aircraft flying around.

You are correct, it would have to be an unusually low pressure, but Zooker's statement that it is 'not used in the UK' is factually incorrect in so much that it could feasibly be used given the right aircraft/pressure/airfield combination...

[ZOOKER]

anotherthing,
Never heard it on the R/T, but I bow to your superior knowledge. You learn something every day!
Airfield, in T'Rossendale Valley? Ecky thump!! Does O'Leary know about this? :}

[NBanker]

I see your Rossendale and raise you Treborough at 1200ft amsl
Fold. Didn't know there is an airfield at Treborough. One lives and learns.

Zooker's statement that it is 'not used in the UK' is factually incorrect in so much that it could feasibly be used given the right aircraft/pressure/airfield combination...
Fair enough.
NB

[ZOOKER]

On 22/12/1926, John Leeming and Bert Hinkler landed an Avro585 Gosport on the summit of Helvellyn (elevation 3,117ft amsl). After a short stay they returned safely to EGCD, thus forever eliminating Treborough as the highest UK 'aerodrome'. :E
Now I bet they used QNE!

[wings folded]

on the summit of Helvellyn (elevation 3,117ft amsl).


In younger and fitter days I used to be able to climb Helvellyn, but I remember it as being 3,118 ft AMSL.

Wiki whotsit says you are right, but I was just wondering if it had sunk a little bit in the meantime.

It is quite heavy after all.

And, yes, I have been to Barnsley, and Yarmouth, and Chatham

[ZOOKER]

wings folded,
Strangely it is not as heavy as you would expect.
Check out the results of M.H.P. Bott's 'Gravity survey of The English Lake District and Vale Of Eden (1974). - All down to an enormous Granitic intrusion, apparently.
It was 3,118 ft, but I suspect modern surveying methods are more accurate.
Hope AW doesn't spot the reduction in elevation.

[wings folded]

Hello Zooker,

I hope other dear readers will allow this slight diversion from the main topic.

It probably is not as heavy as I expect, but remains, in my view, soddin heavy. Couldn't pop it in my shopping trolley.

But you reassure me; I was starting to think that MSL had risen by one foot, perhaps. We hear so much about global warming, ice cap melting and so forth......

Is AW the great Arthur Wainwright by any chance?

[ZOOKER]

wings,
Nearly, it was actually 'Alfred' Wainwright.
You may be confusing him with William Arthur Poucher FRPS. WAP did for Lakeland photography what AW did for drawing and topographic description. Both were top men.
Poucher's books, are all out of print, but well worth sniffing out.
Oddly in 'The Lakeland Peaks', Poucher suggests that climbers should carry an 'aneroid', or altimeter.
Isn't that where we came in?

[Sideshow_90]

if an American requests QNH in inches you remind them it is there job to convert

[ZOOKER]

Slideshow,
Whatever happened to "Tuned in to your customers"?

[wings folded]

Thanks Zooker.

No confusion with WAP; just a shoddy lapse of memory.

Wainright was born in the same town that I was.

But I fear we are becoming tedious for other readers of the thread.

So, to drag things back to the OP's question, another suggestion.

Buy an altimeter off ebay, or beg one off your flying school, or by whatever means, get hold of one.

Establish your height AMSL (OS maps help a lot).

Wait for stable anticyclonic conditions during which you can calibrate your altimeter by reference to your pressure on that day as given by the official Met.

That means set your your AMSL height on the main scale, and fiddle around with the subscale till you have the regional QNH. (You have to disconnect the subscale machanism - methods differ according to the make)

You now have a super precise barometer.

Visitors do not walk up to it and tap it.

When you get up in the morning and you see from your altimeter that your house has sunk or risen, as the case may be, but by recalibrating to your known height, you get your local QNH, but above all, you get a sense of familiarity and comfort with altimetry.

Good luck with your studies, and I hope you will be a happy and safe aircraft driver.

[2 sheds]

That means set your your AMSL height on the main scale, and fiddle around with the subscale till you have the regional QNH. (You have to disconnect the subscale machanism - methods differ according to the make)



What...??!

[wings folded]

2 sheds

When folk say "What?" to me I usually think it is one of two possibilities:

1) Lack of comprehension
2) Deafness

As we are in written form, I will rule out 2)

So, we are down to lack of comprehension.

Was it my finger / keyboard dyslexia trouble with the word "mechanism" which upset your comprehension?

Please do enlighten me.

[Glamdring]

He means that being second hand the altimeter will need calibrated. This involves being at a known height and having a known QNH. You then set both of these on the altimeter (With the subscale disconnected from the main scale), reconnect the scales and voila, your altimeter is calibrated.

[wings folded]

He means that being second hand the altimeter will need calibrated. This involves being at a known height and having a known QNH. You then set both of these on the altimeter (With the subscale disconnected from the main scale), reconnect the scales and voila, your altimeter is calibrated.


Thanks Glemdring.

I was genuinely confused by the rather curt response from 2 sheds, but I see that at least you comprehend.

And of course, for an aircraft mounted altimeter in active service, pilots are not authorised to do the calibration; you need a licensed engineer.

Funny that, you are trusted to fly a potentially dangerous bit of kit but cannot carry out a simple alimeter calibration....

[2 sheds]

Wings

Sorry - didn't intend to be curt, just to query the logic of calibrating against a RPS - that would not ensure accuracy.

Rgds

2 s

[wings folded]

No need to apologise 2sheds.

My suggestion of waiting for a stable anticyclonic system was to cover the snag that the regional QNH may vary from your location's QNH.

I happen to be close to an airport at the same elevation as me, so my local QNH is a good reference.

If that is not your set up, a good anticyclonic system with wide spaced isobars allows you to calibrate your altimeter from the regional (even Barnsley, for goodness sake) since the regional and your local QNH will be the same in a stable met condition.

Otherwise, what do you think of my suggestion?

I have an altimeter in my home which serves as a domestic barometer.

I happen to appreciate precision instruments in themselves, but when they are furthermore actually useful, I think that there is a double advantage

[DFC]

Here is something that does not appear to be covered but should be;

ABC airfield elevation 0ft

South of ABC is a hill 1000ft AMSL

Minimum Altitude to vector aircraft south of ABC is 2000ft

What is the minimum altitude the radar controller can descend an IFR flight being vectored south of ABC when the OAT at airfield is Minus 5C?

How would the answer change if the airfield had an elevation of 500ft but everything else remained the same?

Regards,

DFC

[ZOOKER]

DFC,
Interesting one. Are we talking 'D' Values here?

[DFC]

Are we talking 'D' Values here?


No. If you mean what I remember D values to be used for we would be talking about pressure pattern navigation.

The answer is actually quite simple if one uses either the table provided in the AIP or the rule of thumb provided in ICAO DOC 8168 Vol 1.

Regards,

DFC

[NIFTY SO AND SO]

Altimitry???

FROM HIGH TO LOW LOOK OUT BELOW!

Always served me in flying and ATC.

Cheers folks!