View Full Version : Using Altitude Alerter at Transition

24th Apr 2010, 14:15
On less sophisticated aircraft which do not have bells and whistles to notify pilots that the aircraft is passing or approaching the transition altitude/level, has anyone heard of the basic altitude alerter being set to the transition altitude/level so the audible chime acts as a reminder to set the altimeter to standard or QNH or vice versa? Any pro's or cons (dangers) of using this method?

24th Apr 2010, 15:06
While I only have first-hand experience on few airliners, I have never heard of an alert announcing the passing of the transition altitude. In my opinion, such a system would be plagued with one major problem: the transition altitude is not at a fixed value all over the world but is subject to national airspace structure and also the terrain situation around the field. For example, in VIE it is at 5000ft while a few miles further east, Hungary uses 10.000ft. IIRC, Innsbruck has 10.500ft and nearby Salzburg uses 4000ft. So I think it is sufficient to have the trans. alt noted on the charts for instant reference - these are on the yoke anyway when departing/arriving. Same with the Transition Level, which takes the QNH and OAT into account on top of the Trans. Alt. and is delivered by ATC usually either via ATIS or in a descent clearance. Now, setting the Trans. Alt in the Altitude Alert System would lead to two things: firstly, the airplane would level off at the selected alt., which it is not supposed to do most of the time. Secondly and most importantly, this leaves the probability for a level bust at the actually cleared Alt/FL. Resetting the selected Altitude to where ATC wants You to go after transition sounds rather error-prone. In case it might be forgotten to switch altimeters right at the correct altitude/FL, this action is linked to the Climb and Approach checks in my company to provide a subtle reminder and this system seems to work just fine.

24th Apr 2010, 15:34
Boeings (737, at least) have an "ALT DISAGREE" indication if you are still in QNH if you pass the transition level on climb out. The reverse is true on descent.

Although, you're right - it is variable, but when you select SIDs STARs or approaches, it automatically inserts the expected transition level. Otherwise it defaults to FL180.

I wouldn't do it as you suggest, Freo, simply because the threat of leveling off at cruise in QNH is less than the threat of leveling off at the wrong FL because you didn't set it originally and leveling off mistakenly at transition level in mountainous areas could be deadly.

24th Apr 2010, 17:28
During descent, it's easier just set QNH whenever you're cleared to an altitude, instead of waiting until you're exactly passing T/L; and during climb, set QNE whenever you're cleared to a Flight Level, instead of waiting until you're exactly passing T/A. . . ? That way you don't need to set any "reminders." :{

Pilot Positive
24th Apr 2010, 17:41
I would suggest that it could be an extra unneccesary dynamic and could be misleading in a busy multi-crew operation unless it forms part of your company's SOPs and you have been trained this way.

Best bet is to make it part of the departure/arrival briefing and get the PNF to call TA on reaching/passing. Some companies use MSA as the trigger to set standard when cleared to a FL on departure.

Whilst in the descent set QNH (maybe already have QNH set on the standby altimeter when you initially get ATIS?) and go into approach checks when advised to descend to an altitude by ATC. :ok:

24th Apr 2010, 17:57
rather than the bespoke TA/TL's favored by some.

galaxy flyer
24th Apr 2010, 18:40

I agree and cannot understand why so many pilots are hung up on changing over EXACTLY at the TLv or TA. Just change to QNE when assigned a level and QNH when assigned and altitude. Simple and prevents level busts. IF ATC changes their mind and reclears to a level or altitude, change back, as appropriate.


24th Apr 2010, 22:16
Spot on GF.

I have always done the same as you suggest. If you have a third 'standby' altimeter, you can always leave it on QNH until you are through T.Alt, in case you need a quick check on your altitude after you've set STD.

One small nerdy gripe: My understanding is that 1013.2/29.92 is not 'QNE', it is 'Standard Altimeter Setting'.

QNE is the reading on the altimeter when you are on the airfield with STD set. In other words, QNE is the pressure altitude of the airfield.

I've never used it but apparently its purpose is that it may be used at times of very low atmospheric pressure when it may be impossible to set QNH. The airfield broadcasts the 'QNE' and you set 1013.2/29.92 and add the procedural heights to this value in order to fly the approach (I think). Has anybody else come across this?

Whatsit Doingnow
25th Apr 2010, 05:08
Boeings (737, at least) have an "ALT DISAGREE" indication if you are still in QNH if you pass the transition level on climb out. The reverse is true on descent.
I'm not sure which 737 you fly ImbracableCrunk but on the one I fly the ALT DISAGREE message only appears when there is a difference of more than 200 feet between captain's and f/o's altimeters.

If you pass transition altitude without setting STD then the QNH or QFE setting will turn amber and become boxed, and likewise on descent the STD will turn amber and become boxed if you forget to change at transition level.

25th Apr 2010, 12:54
You are correct. Thanks.

capt. solipsist
25th Apr 2010, 14:40
Just do whatever is in your SOPs. If you do it often enough, the chances of forgetting it decreases.

Same principle applies with "prepare cabin for landing" commands during descent. Once you do it often enough, you only forget it half the time, not 90% of it :E

Anyway, that's why there are 2 badly-paid pilots in the cockpit: to remind each other what they themselves have forgotten :ugh:

27th Apr 2010, 08:02
galaxy flyer and glueball
If ATC ask for your altitude or level passing for separation purposes, what would your delay in response be?

galaxy flyer
27th Apr 2010, 12:41
As Wingo Wango says, besides at below TA levels, the climb rate will make any report obsolete in moments anyway; ATC does not need a altitude passing report within 100 feet. It would take a difference between QNH and STD of .5 inches to be a factor.


27th Apr 2010, 15:53
If ATC ask for your altitude or level passing for separation purposes, what would your delay in response be?

harrowing, maybe the rules are different in Australia but here is what the UK does:-

From the UK AIP:-

The vertical position of an aircraft at, or below, any Transition Altitude will normally be expressed in terms of Altitude. The vertical position at, or above, any Transition Level will be expressed in terms of Flight Level. When descending through the Transition Layer the vertical position will be expressed in terms of Altitude, and when climbing terms of Flight Level.

Later in 5.1.4.

Where cleared for climb to a Flight Level, vertical position will be expressed in terms of Flight Level, unless intermediate altitude reports have been specifically requested by Air Traffic Control.

5.3 Approach and Landing

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.

Altimeter Setting Procedures (http://www.nats-uk.ead-it.com/aip/current/enr/EG_ENR_1_7_en.pdf)

30th Apr 2010, 10:52
eckhard: ...common usage accepts QNE as the ISA Standard Pressure setting of 1013.2 hPa, or 29.92 inches, always set above T/A.

Another definition of QNE that you are referring to is the 'altitude displayed on the altimeter at touchdown with 1013 set on the altimeter sub-scale'. It is also known as the "landing altimeter setting."

Within the latter meaning, the term would be of use when an extremely low QNH is outside an aircraft's altimeter sub-scale range, and the pilot requests aerodrome QNE from air traffic services. But such extreme atmospheric conditions occur primarily near the core of a tropical depression/cyclone/typhoon; where airplanes wouldn't be operating.

QNE can be calculated by deducting the QNH from 1013, multiplying the result by 27 (the appropriate pressure lapse rate per hPa) and adding the airfield elevation.

For example: QNH 960 hPa, airfield elevation 500 feet, pressure setting 1013.
QNE = 1013 960 = 53 27 = 1431 + 500 = 1931 feet (the reading at touchdown).

2nd May 2010, 12:59
Thanks Glueball, that's how I understand it as well.

QNE may also be of use during very high atmospheric pressure, although one procedure that I saw told pilots to set the upper limit of QNH on the altimeter and just accept that you would be higher than indicated (= a 'safe' error). I guess it's only safe under IFR if all the aircraft have the same altimeter setting.

I think most modern altimeters are adjustable from 950-1050 hPa/mb, which should cover 99.9% of occasions; however, from wikipedia:

The highest barometric pressure ever recorded on Earth was 32.31 inches (1094hPa), measured in Agata, U.S.S.R., on December 31, 1968. Agata is located in northern Siberia. The weather was clear and very cold at the time, with temperatures between -40 and -58.

The lowest pressure ever measured was 25.69 inches (870hPa), set on Oct. 12, 1979, during Typhoon Tip in the western Pacific Ocean. The measurement was based on an instrumental observation made from a reconnaissance aircraft.

Anyway, I agree that QNE is in common usage to mean 1013.2/29.92, but common usage doesn't make it right! Just look at all the supermarket check-outs with '10 items or less' displayed! How many times have you heard pilots refer to tracking a 'radial' from an NDB?

I am realistic enough to admit that the risk of misunderstanding is small in the case of QNE and that it doesn't really matter. Language evolves and all that, but it still grates a bit!

Actually, imprecise language can have safety repercussions. The Dan-Air 727 at TFN hit the terrain in the holding pattern because the controller said, 'Turn left' instead of, 'Left turn'.

What he meant was, 'Enter the hold, and once established, fly a pattern with left turns'.

What the Dan-Air crew understood was, 'When you reach the beacon, enter the hold by turning to the left'. A tragic misunderstanding.

I once had a co-pilot who read out part of a SID as follows: 'Turn at the latter of 1500ft or 2 DME'. He didn't see the joke when I replied, 'So turn at 2 DME then? Why bother mentioning 1500ft at all?' What he thought he'd said was, 'Turn at the later of 1500ft or 2 DME.'

There have been several cases of patients being injured or worse, when doctors whose first language is not English became confused over the meanings of 'prescribed' and 'proscribed'.

OK, rant over. I'll crawl back under my rock!

capt. solipsist
17th May 2010, 09:03

The way we use QNE is NOT common usage, it is the PRESCRIBED usage. Not because people commit mistakes in usage mean we should just all follow them.

There is a reason why ATC language is quite use-specific.

As well, just because somebody is a native English speaker doesn't mean he's already proficient in ATC comms. Quite the contrary, I'd say.

Some of the pilots I know who had a very hard time being word-perfect in ATC phraseologies are native English speakers.

Why try to be word-perfect? 3 letters: CRM.

Cheers!!! :ok:

17th May 2010, 09:25
The best altitude alert is good CRM, and good airmanship which is enhanced and informed by a good, thorough briefing by both pilots prior to departure or arrival, and then good scan, and good monitoring by the monitoring pilot.

The second system can be fitted in aeroplanes fitted with EGPWS that has a GPS feed, either from the aeroplane's fitted GPS or from a GPS card in the EGPWS. There is a database that has all the currently known (by the manufacturer) transition altitudes, and levels for all the currently known, and included in the database airports in the world. The accuracy of the information that your EGPWS gives you relies on your airline updating the database in the EGPWS. In the case of Honeywell systems the updates are available at no charge for your airline to download from Honeywell, and to update as they are released. The information in the data base is gathered by Honeywell from AIPS and so on, so relies heavily on the AIP being updated and amended correctly by the National Authority, so the first paragraph now applies again.

The altitude alert is only an aid to situational awareness, and will never beat good airmanship, and good flight deck practices.