ALT Setting procedures

[Marant]

Help, tell me I'm not going senile.
Have recently started a new job in another country and the Company SOP's tell us to reset to area QNH at 1000ft below intended cruise altitude. All our op's are conducted below Transition (DHC-6) and we normally level off at about 8 or 10,000 at about 15 or 20 dme. I recently had on 3 days running, Radar question the integrety of our transponder then asked us to switch it to mode A. They even gave us the Terminal QNH but my training Capt (young upstart) refused to change back as it was Company SOP's to change already (to area QNH). Difference on the days mentioned was either 5 or 6 mb's.
It's my understanding that if you are in a TMA or control zone then you set the QNH as advertised on the ATIS or as informed by ATC. Area QNH is exactly that...Area QNH as against Terminal QNH.

Can anyone point me to an ICAO reference that I can refer to and quote to our FOM so as to get this sorted out. I'm unable to find anything in writing myself. Because FOM couldn't find anything in our AIP then he said SOP's remain unless I can show him an alternative, In the mean time, our engineering dept is running out of Transponders to replace the ones being written up!!!

[rudderrudderrat]

Hi Marant,

No - you are not going senile.

If you are under radar control - then it's ATC's responsibility to pass the QNH and it's your's to comply by setting it.

[Marant]

Thanks RRat. But I need some official reference...can you believe that common sense just isn't enough these days !. I've searched the ICAO website but can't find it in writing.
Anyone else got advice or suggestion on this one?
Cheers.

[ATCast]

But I need some official reference...

Look in ICAO doc 4444 (PANS ATM) and doc 8168 (PANS OPS).
I am sure there are more than a few lines in there regarding altimeter settings.

[Marant]

Thanks ATCast, read through there and still found nothing.
I'm looking for something that specifically states, when an aircraft is in a particular Airspace, then the Pilot must have a QNH setting set for that particular Airspace.
So far I'm unable to find it, any other ideas?

[rudderrudderrat]

Hi Marant,

All I could find was this for flight outside controlled airspace within the UK. DAP_ACD_Altimeter.pdf (http://www.caa.co.uk/docs/64/DAP_ACD_Altimeter.pdf)

However, if flying within controlled airspace then we obey what ATC tells us with regards Altitude and QNH setting - else it's not controlled. Is your company doing everything VFR?

[BOAC]

Cannot help with any reference, but if you are still in the TMA when you reach 1000' below you SHOULD be on Terminal QNH I would have thought. Once outside Terminal airspace area would be logical. There seems little point in snagging the transponders since you all appear to possibly be flying at the wrong altitude! I thought also that Transponders used their own 1013 independent module for readouts and that ATC converted the reading to QNH if required?

[AerocatS2A]

Yeah the transponder sends altitude reference to 1013.2 hpa and then the software at the ATC end adjusts for QNH. Still, if you have the wrong QNH set then it will display as an incorrect altitude to ATC because their QNH correction is not the same as what you are using.

[BOAC]

if you have the wrong QNH set then it will display as an incorrect altitude to ATC - the point I am making is that as far as I can tell the a/c is at the wrong altitude. Forget what is 'displayed'

[AerocatS2A]

Yes. It is at the wrong altitude and displays to ATC at the wrong altitude, the fact that the transponder sends a 1013 signal is kind of irrelevant because the end result is the same.

We are in vicious agreement ;).

[ATCast]

From PANS-OPS (8168)

The pilot-in-command is responsible for the safety of the operation and the safety of the aeroplane and of all persons on
board during flight time (Annex 6, 4.5.1). This includes responsibility for obstacle clearance, except when an IFR flight
is being vectored by radar.
(Emphasis added by me)

Also from PANS OPS (8168)

The adequacy of terrain clearance during any phase of a flight may be maintained in any of several ways,
depending upon the facilities available in a particular area. The recommended methods in the order of
preference are:
1) the use of current QNH reports from an adequate network of QNH reporting stations;
.....
(Emphasis added by me)
So it is recommended to use the current QNH. The meaning of "adequate network" can be debated, but clearly for ATC it means that if they provide you with QNH, the altitude clearances they issue are related to that QNH.

PANS ATM:

VERIFICATION OF ACCURACY OF MODE C-DERIVED LEVEL INFORMATION
....
3. If the displayed level information is not within the approved tolerance value or when a discrepancy in excess of the approved tolerance value is detected subsequent to verification, the pilot shall be advised accordingly and requested to check the pressure setting and confirm the aircraft's level.
...


Maybe there is strictly speaking no obligation to use the QNH for the airspace you are in, but just choosing the QNH you like for that day isn't exactly a demonstration of good airmanship, nor being cooperative with ATC.

I hope you manage to talk some sense into the FOM. Good luck.

[Marant]

A big thanks to all of you, I can see we are all in agreement, but still hard to find the exact wording I'm looking for, I'm back to work next week and have now decided maybe the only way is to approach them is through National DCA. We're talking PNG here so it may still take a while!
Again, thanks for comments.