When to set STD on altimeter
 

Hi all, I would like some help here. When flying in Europe and taking off from an airport and leveling off ay 3000 ft, the next ATC instruction is climb to FL 210. The TA for the area is 6000ft. For discussion sake, my colleagues are saying that when I am "cleared to" FL 210 that I should make the change but I believe that I should change to STD when passing through 6000. Can someone point me in the right direction. I would like to find the correct procedure, not just a good technique. Thanks in advance.

Correct procedure is what is in your OM-A-chapter 8 and/or OM-B/FCOM.

Set to STD when passing through Transition Altitude on the climb (6000' in your case). Set to QNH when passing through the Transition Level on the descent. If ATC needs to vertically separate you and another a/c whilst you are both in the Transition Layer, ATC will issue you both with the same pressure datum to effect that separation.
Do NOT set STD (even if cleared to a FL) if you are below the Transition Altitude

I would say, whatever your company says !

However, having been on the ATC end of some spectacular level busts with climbing aircraft failing to set Standard Pressure, I would say, once cleared to a FL on the climb set 1013, once cleared to an altitude on descent set the QNH (which you will have just read back).

In all my years at Prestwick Centre up until my retirement in 2016, I have only been asked for the Transition Altitude or Level on a handful of occasions, but we had a handy table of minimum usable levels according to the pressure, so it was all pretty academic most of the time, under radar control we ensured separation and terrain clearance.

Having managed to blag my way onto many jump seats over those ATC years, mostly European airlines, I cannot recall ANY pilot calling out "passing transition altitude/level, setting 1013/QNH" but I do remember seeing them do it once cleared to a FL or altitude and both crew setting altimeters and cross checking.

Outside Europe where transition altitudes/levels are as high as FL180 you MUST set STD or QNH at the transition altitude/level and not before
You should not set it when cleared, as in the UK. At our airline we call passing transition both up and down and carry out an altimeter check.
Operating into UK airports we set it when cleared, as described above.

As an ATCO I'd expect you to set the relevant pressure (STD or QNH) as soon as I clear you to a FL or an altitude - at that point I'm not relying on vertical separation against other traffic anyway.

I am aware that a number of airline SOPs require you to wait until the TA/TL before doing so - also not generally a problem for me as per separation comment above. However...

A friend used to fly heavies for a certain airline, which mandated waiting until TA/TL to change the pressure setting - I remember him warning me about the very significant risk of a major level bust in the descent if the QNH was low, and was always cautious about descending them to 1000' above anyone else in that scenario.

The airline with the largest presence in the skies over Europe has a standard procedure to set STD/QNH immediately when cleared to a FL/Altitude. Within the UK, at least, they have the best statistics for level busts. Now, that's probably the result of a combination of strict SOPs, but it does support the theory that it's better to make the change immediately.

I can certainly see an argument for leaving the standby altimeter in QNH in the climb, at least until MSA or TA as we often get contingent clearances at low altitude; for example: 'On reaching 6,000 feet cleared direct XXXXX', in which case having a reference to the altitude is useful.

But I don't think it is necessary to stay on QNH until the TA. In the aforementioned company the SOP where one is passed a 'stop climb' by ATC is to immediately press Altitude Hold, set the new clearance and then Level Change on the Autopilot. If the new cleared level were actually an altitude, the pilot would simply press a single button to return to QNH after selecting the new altitude, and before selecting Level Change. It would make no practical difference to the risk of a level bust.

In Argentina we make the change during climb ONLY after crossing the TA (even if we were cleared up to a FL).

Its clearly stated that it should be done only in this fashion in the AIP under ENR 1.7 (spanish only).


The only exception is when you are cleared for an approach. In this case, you can make the change from QNE to QNH while above the transition level (instead of after leaving it) if you were not instructed to maintain a level above the TA.

Australian AIP ENR 1.7 commencing at para 2.1; requires 1013.2 to be set passing A100 on climb and QNH to be set just prior to entering the transition layer - normally F110.

That's quite correct. ATC can be using your Mode C or ADS-B level for vertical separation with other traffic. (Disclaimer - apparently not so in Nudging's unit) If you have 1013.2 set below the transition level, or QNH set above it, then your reported level/altitude will be incorrect, and increasingly incorrect as QNH varies more from 1013.2. ATC only applies a 200ft buffer to these reported levels for separation purposes. Obviously this buffer is negated if using the wrong pressure setting and QNH is more than 6 hPa different from 1013.2.

Correct me if I'm wrong, but I thought the transponder always reported altitude with 1013 as its datum, regardless of what QNH has been set on the altimeters?

Edit: Just re-reading @parishiltons post, and realised that you were perhaps referring to levels/altitudes reported by the pilots rather than the transponder, in which case your comment makes perfect sense, and I was being a numpty.

I worked for a very long time in companies that required us to stay on QNH until passing TA in a climb, which is easy enough, you get warned about that on the PFD anyway (yellow QNH on boeing, blinking on airbus). However, during descent we had to set QNH as soon as we were cleared to an altitude. Now i'm working in a company that requires us to the set the cleared pressure datum once cleared there (standard for FL, even with high transition altitudes, QNH for altitudes).

Both works, and the only level bust i have seen was reverting a clearance to altitude once already on standard and due to a large spread in pressure already being above the cleared altitude.

In the UK 'QNE' is not an altimeter setting. It is the reading in feet on an altimeter with the sub-scale set to 1013.2 hPa when the aircraft is at aerodrome or touchdown elevation. it is used during conditions of exceptionally low atmospheric pressure when it is not possible to set QFE or QNH on some aircraft altimeters.

To clarify

ATC systems correct reported level for QNH below the transition layer. So if two aircraft are operating below the transition layer at the same vertical distance above ground, one has 1013.2 set and the other QNH, then they will display different altitudes to ATC. So for example if the transition layer is A100/FL110, then FL070 will display as something other than 7000 to ATC, the size of the difference depending on the pressure difference between QNH and 1013.2.

For this reason other AIPs at ENR 7.1 (not just in Argentina) require QNH to be set when operating below the transition layer.