When to set STD on altimeter

[hawkerjet]

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.

[Dufo]

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

[uncle dickie]

Keep it simple and safe. Set STD when cleared to the first FLIGHT LEVEL.
Why wait until 6000ft?
Once cleared to FL210, won’t ATC expect any level information requested by based on STD.
Your mode ‘C’ is seen by ATC anyway.

[CEP]

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.

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

[The Fat Controller]

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.

[Smithy02]

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.

[wiggy]

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

Do you have a reference for that?

It seems that In common with many others our Ops manual is very prescriptive in requiring STD to be set on the PFD once cleared above the transition altitude regardless of whether the TA is low or high...(the standby alt is left on local setting until passing the TA).

[172_driver]

We set STD as soon as we are cleared to a Flight Level.
If cleared to a FL before take off we set STD once the flaps are up ("Flaps are up", used as a trigger)

I didn't think anyone did it significantly different, seems I was wrong.

[NudgingSteel]

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.

[Piltdown Man]

Except at MME. I was badgered throughout the climb for “altitude” but the lady insisted on altitude. Otherwise I would agree.

PM

[good egg]

It seems that In common with many others our Ops manual is very prescriptive in requiring STD to be set on the PFD once cleared above the transition altitude regardless of whether the TA is low or high...(the standby alt is left on local setting until passing the TA).


That sounds like good practice to my (ATC) ears. There is always the possibility that if ATC has climbed you from, say, altitude 2000ft to, say, FL100 that ATC might spot a previously unseen confliction and say “Stop climb at altitude 6,000 ft”.

At least with Standby Alt in local setting you have the correct reference available to either manually stop (if close to the stop altitude) or to “tinker with buttons” if there is time?

Is that too simplistic? (Will have to check on next fam flight!)

[Mikehotel152]

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.

[casablanca]

My company policy is approaching TA....generally 1000 feet before.
be careful at some airports with low altitude level off, example TA 3000 and cleared to FL 040.
if there is a big change in altimeter setting between Qnh and standard, like 995 going to 1013 the altimeter makes an abrupt jump and may not allow time to level off.

[RBF]

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.

[topdrop]

Do you have a reference for that?

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.

[parishiltons]

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.
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.

[am111]

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.

[Denti]

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.

[Talkdownman]

you can make the change from QNE to QNH while above the transition level
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.

[parishiltons]

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.
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.

[tescoapp]

It's a strange one this because in quiet a few caa and aip's the pilot and ATC internal dept are completely at odds with each other. I have worked with sops written as per UK method and approved by foi. But aip and ATC expect Change at transition. I did ask and was told not to worry about it ATC were run by the military and were clueless.

Even in Europe there are 4 different ways of doing it in aip's. Pilots do not read aip's as a rule.

Personal experience looking at a fleet of 20 aircraft and 60 pilots says there are more alt busts changing at transition. We had a group that were adamant to change at transition and a group that changed when cleared The first group accounted for 95% of the busts. The second did have a couple of busts but they were going to happen what ever the setting was being told to level off with less than 500 ft to go and climbing at 2500ft per minute.

[wiedehopf]

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.

This is incorrect. The altitude is always broadcast independent of aircraft altimeter setting.
Why would you design the system to potentially transmit a bogus altitude because the pilots set the altimeter wrong?

Wikipedia can be a bad source so google "mode c pressure altitude" because that is what is transmitted, the pressure altitude.

And the pressure altitude is independent of the local pressure. Then the ATC system corrects for local pressure and voila you get a correct readout.

Now the number on the planes altitude indicator may be different from the one displayed on the ATC system because the pilot already set standard pressure. But that's not a problem is it?

[parishiltons]

This is incorrect. The altitude is always broadcast independent of aircraft altimeter setting.
Why would you design the system to potentially transmit a bogus altitude because the pilots set the altimeter wrong?

Wikipedia can be a bad source so google "mode c pressure altitude" because that is what is transmitted, the pressure altitude.

And the pressure altitude is independent of the local pressure. Then the ATC system corrects for local pressure and voila you get a correct readout.

Now the number on the planes altitude indicator may be different from the one displayed on the ATC system because the pilot already set standard pressure. But that's not a problem is it?
OK we're going a little off topic here so I won't prolong the thread too much. Let's look at it the other way around. Example: Two aircraft operating below the transition layer, both indicating 7000 by altimeter, regardless of whether cruising or climbing/descending. One has QNH set, the other 1013.2. The one operating on QNH will correctly display 7000 to ATC, the one operating on 1013.2 will not, due to the QNH correction applied by the ATC system. ATC allows a 200FT tolerance to verified levels. In other words, if a pilot reports at 7000, then so long as the display to ATC shows 6800 to 7200, then the report will be accepted as correct.

So coming back on to topic if there is other traffic at 8000 or 6000 on QNH above or below the aircraft operating on 1013.2 at 7000 and the pressure difference between QNH and 1013.2 is > 6HPa the wrong way then the aircraft on 1013.2 will be deemed to be in vertical conflict (assuming a 1000FT vert separation standard is applicable). Similar applies to a climbing flight that sets 1013.2 while still below the transition layer. That is the reason why climbing flights should not set 1013.2 while still below the transition layer.

Oh, and let's not get hung up about Mode C (or even Mode S, for that matter). Radar is a dying technology, rapidly being replaced by ADS-B and with accelerating pace of technology change who knows what next.

[tescoapp]

The situation above would only be possible when the aircraft is fitted with extremely old first generation encoding altimeter with a first generation mode C transponder. Your talking about a 40 year old setup.

Transponders have had their own pressure cell since then and it will only squirt the pressure on 1013. What the pilots altimeter settings are makes not the slightest bit of difference.

The transponder is calibrated every 3 years for IFR machines.

The only aircraft that are even remotely likely to have an encoding altimeter transponder setup will be privately owned antiques with old none digital transponder selectors, Russian or Military.

If its a digital display it will have its own pressure cell for the altitude data.

Those are standalone transponders.

For air data computer machines the transponder can get the data from the data bus in its raw state ie 1013.3 and uses that and the EFIS system converts the same data for QNH for display to the pilots. But again what the pilots set won't change what the transponder transmits.

Most digital transponders be it S or C allow you to see what it is transmitting. Just fly manual and select it and fly level on the backup altimeter and wind the QNH up and down on the main altimeter, the value shown on the transponder won't change.


There is also a theory out there which I think does come from Australian expats is that you have to be very careful and slow changing between standard and QNH and vice versa and not to use the press for standard button (which you must use your finger not your thumb to press) because the sudden change in value might trigger a TCAS event. Complete ignorance of altimeter systems, but they are adamant that you have to do it that way and change at transition.

[Doc Holliday]

I would set standard when I have been cleared to a FL and once above the MSA most of the time, however, Some SID's have not below altitudes for terrain clearance even though the final level is a FL. So for navigation purposes I would want QNH set for longer. If the final level on a SID is a low FL in an area where the transition altitude is low, you may want to set Standard soon after take off especially when there is very low pressure as setting it late could result in an alt bust. I don't believe there is a single rule that will cover all situations, we need to use common sense and airmanship as each departure is different. In the UK when cleared to an altitude in the descent we tend to set QNH straight away, this never seems to be a problem. When in Europe the controllers seem to expect you to set QNH when passing transition level and not before. Out of interest what do you call standard once you have set standard? "Standard" or "one zero one three" or "ten thirteen"

[topdrop]

Three aircraft below the transition altitude, A is 7000ft above 1013 pressure level, B is 7000ft above 1000 pressure level - the current QNH.
A's transponder will be sending 7000 to radar, B's will be sending 7390. These figures are then corrected on ATC display to show A as being at 6600 (his actual altitude above the QNH pressure level) and B at 7000.
Aircraft C is opposite direction at 6000 on QNH. Good chance for breakdown of separation with A, as A has the incorrect pressure set on altimeter.

[topdrop]

Transponder transmits with reference to 1013mb.

The figures I posted re transponder transmission are reference to 1013 - I am not sure what you are trying to say.

[The Fat Controller]

@topdrop, in your scenario, if it was in CAS then ATC would have everybody on QNH.

If A had been cleared above TL and had set 1013 but subsequently had been "stopped off" then ATC would ensure QNH is passed again.

Any incorrect altimeter setting has potential for a loss of separation, full stop.

Personally, since the introduction of RVSM, I very rarely noticed any Mode C with an error of 100 feet let alone the accepted tolerance of 200 in any commercial aircraft,