how to show GROUND in myflights

[dudbaker]

Tom

Just checked London Volmet 128.6, Stansted Atis 127.175 RAF Volmet on 5450 and all giving QNH.  Lippetts Hill police helicopter site is giving QFE. 

Dudley

[viking9]

Tom

Just checked London Volmet 128.6, Stansted Atis 127.175 RAF Volmet on 5450 and all giving QNH.  Lippetts Hill police helicopter site is giving QFE. 

Dudley

Dudley,

In my experience as a pilot (retired now), most general aviation airfields and helicopter operating bases without ILS inform the pilot of the QFE so that he/she can join the circuit at the correct height.

Volmet and ATC services give QNH as they are 'area' based. ATC requires all aircraft to have their barometric altimeters set to the same datum for a particular FIR in order to maintain proper vertical separation. Aircraft also need to know what their height AMSL is as that is what the height of obstacles such as mountains etc is indicated on maps and charts.

Tom

[viking9]

In case others are wondering why the codes QFE and QNH are used, they are part of the three letter 'Q' codes invented when the Morse Code was the primary means of long distance radio communication. Some others are:

QNE - Atmospheric pressure at sea level in the International Standard Atmosphere (1013.25 hPa)
QDM - Magnetic bearing to a station.
QDR - Magnetic bearing from a station.
QFU - Runway in use (e.g. QFU 29 - Runway 29 in use).
QTH - What is your position?
QSY - Change frequency (e.g. QSY 123.40)

and my favourite:

QRM - Are you being interfered with?  :-))

Tom

[tarbat]

A question I've raised before and still puzzles me a bit is what barometric pressure do pilots use to set their altimeter.  I hear ATC telling pilots to set both QNH and QFE.  What rules (if any) determine whether a pilot sets their altimeter to QNH or QFE?

Secondly, is this barometric altimeter always used to set the ModeS/ADS-B altitude, or does this sometimes come from the aircraft's radar altimeter?  This question particularly applies to military aircraft operating low-level.

[dudbaker]

Tom

Totall agree with all that.  I notice that Northweald has a circuit height of 800 aal.  What ever aal is.  Stansted Stars all use QNH.  Stansted Terminal chart gives both.  For overshoot for example.

Tarbat

They all used to use QFE.  Then for a while ATC would ask the captain what was wanted. (Company Policy).  Both were on ATIS but now only QNH.   Now QNH unless radalt problem.  See MEL 34 42 02.  If automatic call out not working operating procedures to be ammended to allow for manual calls.

Now I always thought mode C came from one of the altimters and ATC would see what the pilot sees.  I was corrected by Allocator and Dave Reid, on one of the forums here.  I checked my A320 notes and sure enough the transponer sends Standard.  ie 1013.2.  From the Air Data Computer not Radalt.  Hence,  as you have said on many occasions you need to set QNH on RB either manually or Automaticlly. 

I am asssuming altitude reporting was changed because of a crash into the sea.  Aircraft cleaners had left tape on the static vents.  The pilot new he had a problem so asked ATC for his height.  Unforunatly,  ATC saw the same as the pilot and the aircraft hit the water with a reading 4000 feet.  This may not always help but to you have more than one sourse is better.

It might be fun to set QFE on RB but would not make much diffence where you are. 
Used to come up to Lossie to fly Canberras as silent targets for 8 Sqn Shackeltons. 

Dudley

[Keith L]

Tom

I notice that Northweald has a circuit height of 800 aal.  Whatever aal is. 

aal = above airfield level

[viking9]

A question I've raised before and still puzzles me a bit is what barometric pressure do pilots use to set their altimeter.  I hear ATC telling pilots to set both QNH and QFE.  What rules (if any) determine whether a pilot sets their altimeter to QNH or QFE?

Secondly, is this barometric altimeter always used to set the ModeS/ADS-B altitude, or does this sometimes come from the aircraft's radar altimeter?  This question particularly applies to military aircraft operating low-level.

Tarbat,

I answered your question regarding use of QNH/QFE a few posts back.

I think you will find that the radar altimeter is not reliable above/not used above 2,500 ft. So above that altitude it will be the baro alt that provides the input.

Tom

 

[DaveReid]

I think you will find that the radar altimeter is not reliable above/not used above 2,500 ft. So above that altitude it will be the baro alt that provides the input.

Mode S altitudes (and possibly Mode C, though I'm not sure about that) may alternatively be GNSS-derived.

[dudbaker]

I checked my A320 notes and sure enough the transponer sends Standard.  ie 1013.2.

There is a switch on the transponder marked - Alt Rptg or off.  The note that goes with the switch says - Baro standard data is transmitted.

Dudley

[mdobuk21]

cheers guys for the excellent help!

mark

[dudbaker]

Hi

Found this.  http://www.nats-uk.ead-it.com/aip/current/enr/EG_ENR_1_7_en.pdf

5.3.1 When an aircraft is descended from a Flight Level to an Altitude preparatory to commencing approach for landing, ATC will pass the appropriate aerodrome QNH. On vacating the Flight Level, the pilot will change to the aerodrome QNH unless further Flight Level vacating reports have been requested by ATC, in which case, the aerodrome QNH will be set following the final Flight Level vacating report. Thereafter, the pilot will continue to fly on the aerodrome QNH until established on final approach. When requested by the pilot or local procedures require, the appropriate QFE and aerodrome or threshold elevation shall also be given.

Dudley