Primarily for general aviation discussion, but other aviation topics are also welcome.
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When doing circuits, what height setting do you use on your altimeter?

QFE
126
64%
QNH
66
34%
RPS
No votes
0%
I don't look at the altimeter anyway
4
2%
User avatar
By Rob P
#1519198
flyingeeza wrote:.it's reading around 40 feet low despite all the hype about QFE being so important near the runway.


OMG!

How many died? That is just a disaster waiting to happen. :shock:

Forty feet! Jeez! Like all of us I am sure, my eyes are normally glued to the altimeter so as to judge roundout.

That's it. I am switching to QNH instantly.

Rob P
#1519203
Dave_Ett wrote:So why is the altimeter 'wrong'?

Didn't they set it, did they set it to the wrong pressure, or that's simply as accurate as it is?

That's precisely why we ignore the altimeter once established on a roughly similar circuit altitude!

Our standard pressure altimeters are never accurate to much more than 50 feet anyway, so it really is a waste of effort trying to set it to some precise setting.

:lol: Rob P...keep your knickers on ffs...there are still some newer folks on here who are interested in a bit of discussion and who might just learn something.
Dave_Ett liked this
By johnm
#1519209
The combination of pressure setting and altimeter can't be guaranteed to get within 50 ft or so.

However as QNH is above a sea level datum it should be stable and so should the elevation of the field above sea level.

That said sea level isn't the same everywhere, though it only varies by inches not feet :D

For VFR flying you don't really need an altimeter in the circuit, and since you need QNH to avoid level busts there's absolutely no point in QFE whatsoever as I keep telling you :twisted:
Flyin'Dutch', T67M liked this
#1519212
Dave_Ett wrote:
Flyin'Dutch' wrote:- Flying using the QNH allows you to gross error check the function of your altimeter before you get going;

Why is that different from QFE then? I was taught to zero the altimeter, add 10mb and check display, then back to zero. Wind off 10mb, check display and then set to QFE / QNH as required.

Flyin'Dutch' wrote:- Flying using the QNH gives you relevant information in relation to obstacles, terrain and airspace around you


The thread is about QFE in the circuit. Don't think anyone is arguing against QNH outside the circuit!?

Flyin'Dutch' wrote:- Flying using the QNH prepares you to fly to/from airfields which are higher than the sub scale lets you wind off


Can you explain this please? ( Yes I know I'm ignoring the point of the thread - QFE in the circuit)

Flyin'Dutch' wrote:- Flying using the QNH prepares you for the day that you decide to continue your training and development and either go and fly on instruments in IMC or strip flying where the QNH is a lot more useful to have than a QFE from an airfield you are not going back to;


What's the reason QFE isn't used when on instrument approach? I would have expected an FD or AP to want to know when touchdown was imminent by knowing 0 feet = runway. (Again ignoring the point of the thread - QFE in the circuit)

Flyin'Dutch' wrote:- Flying using the QNH makes you more weather aware.


How does it help more than QFE in the circuit?


1. I know what sort of QNH to expect from the METARs of surrounding reporting stations so when I dial in the airfield elevation onto the altimeter I can check the QNH in the Koll's window

2. Go and fly from strips and airfields which are higher than say 1000ft and you cannot wind the Altimeter to show 0ft

3. For APs used to land in 0/0 conditions a radar altimeter is required. In instrument conditions you most definitely don't want to be stooging around on a QFE as it gives no relevant information in relation to obstacles and airspace.

4. Because when you use the QFE you have little idea of what the atmosphere is doing. E.G looking at that video, seeing the sun so low on the horizon and having a QNH of 1038 would make me aware that the fog is unlikely to lift.

Now ignore that this is at Blackpool where QNH is nearly the same as QFE and imagine you are flying to an airfield which has an elevation of 873ft.

If you want to work out what the atmospheric pressure is (and therefore want to know what the weather system is likely to do) you would have to do some mental arithmetic to work that out from a QFE.

Whilst you are doing the sums in your head I can already move on to the next item on the 'to do list'

@flyingeeza - I don't know what you are driving at, you asked what the benefits of QNH over QFE were, I thought I'd given some.

Not sure what the BPL video clarified either.
Dave_Ett liked this
#1519225
Flyin'Dutch' wrote:@flyingeeza - I don't know what you are driving at, you asked what the benefits of QNH over QFE were, I thought I'd given some.


Not me asking FD...I'm one of the >33% who doesn't need QFE, and I know exactly why I don't bother with it. :thumright:
Flyin'Dutch' liked this
#1519231
johnm wrote:since you need QNH to avoid level busts

I know my circuit flying isn't always all that accurate but even I can pretty well guarantee not to be accidentally 6,500' above the nominal circuit height.
Rob P liked this
By johnm
#1519233
kanga wrote:
johnm wrote:..

That said sea level isn't the same everywhere, though it only varies by inches not feet :D ..


er, Barra ? Or even

https://en.wikipedia.org/wiki/Bay_of_Fundy ?

:)



Or even Alderney, but that's tidal, which doesn't affect QNH which uses a standard sea level datum to which I was referring. I first discovered that the datum varies a bit when working on the Channel Tunnel when someone realised they'd have to divert the French end a bit to allow for it :-)
By johnm
#1519236
Gertie wrote:
johnm wrote:since you need QNH to avoid level busts

I know my circuit flying isn't always all that accurate but even I can pretty well guarantee not to be accidentally 6,500' above the nominal circuit height.


A closer reading of my post would show that I pointed out that VFR circuit flying doesn't really need an altimeter at all, but one with a suitable QNH setting is quite important elsewhere, so that's all you need. :twisted:
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