When to go to 1013mb?

[Hoover Pilot]

Greetings,

I would welcome information as to when pilots change from QNH to 1013mb as part of take off SOPs. MY company has recently changed and I wondered how the SOPs compared with other airlines.

Originally our manuals said "when cleared to a flight level, pilots will set 1013 immeadiately". The problem with this method is that after being cleared to a flight level and then instructed by ATC to "stop climb at 3,000ft" you have to reset QNH quickly.

Our new method is to change to 1013 AT transition exactly. The main problem here is that if held at an intermediate altitude for a long time (not uncommon on the Clacton SIDs in the London TMA) the change to 1013 can get forgotten.

I have no experience of operating in areas with high fixed transition altitudes and just wondered how our SOPs compared with others....

HP

[Empty Cruise]

TA - if cleared to FL within 1000 ft. above TA, the altimeter is set to 1013 no later than 1000 ft. below TA.

Brgds,
Empty.

[BOAC]

Small point, but ICAO dictate that the correct setting is 1013.2, not 1013 as many people set, and this is 29.92 exactly, not 29.91. Then you will be on the same setting as the rest of the world :D - in the interests of RVSM, of course! Only around 50ft at high altitude, but we are striving for better height-keeping, are we not?

[411A]

Well said BOAC...and not just when the check pilot is watching either.:E

In all companies that I have personally flown for, the altimeters were set to 1013.2 AT transition altitude, and not before.

[maddog62]

I've seen everything about altimeter settings in the military and in the civilian world.
It looks like nobody's got the perfect solution.
What worked for me the best was PF setting 1013.2 when cleared to a FL and PNF when passing transition.

rgds maddog

[Captain Airclues]

I believe that the ICAO PANS-OPS method is to set the standard setting when cleared to a flight level, although I can't give you a reference until my next visit to the office. The FAA AIM doesn't state when to change, but states that the reported altimeter setting should be used when cruising below 18,000ft and 29.92 inches when cruising above 18,000ft (AIM 7-2-2).

BOAC....On the 744 we just press the button and STD is set, as I'm sure is the case on most modern aircraft. I'm not sure if this sets 1013mb or 1013.2mb, as the baro setting does not have decimal places. However, I make the difference between 1013 and 1013.2 nearer 5ft than 50ft. :)

Airclues

[BOAC]

Cpt A - I guess you base the 5ft on sea level? Try it on your altimeter at 37000' or higher (assuming ythe beast will let you, of course):D I thought for a minute you were going to tell me it was only 0.01 inches:D

FYI - the 'STD' button you quote is also on the BA 737 standby altimeters, and it is a well-behaved, conformist button, setting 1013.2 - which you can see if you have a 'liitle play'!!

Which of course means WE have 2 altimeters on 1013 (29.91) and 1 on 1013.2 (29.92):D

There appears to be a general understanding - in the UK anyway - that the 'standard' setting equates to 29.91.

ICAO refers.

[Captain Airclues]

BOAC

I'm not a technical expert, but I thought that the Air Data Computer took care of that. I will experiment the next time that I'm at FL370 (not in RVSM of course). By your figures the indicated altitude shoud increase by 250ft for each 1mb change in altimeter setting. Will get back to you with the result. :)

Airclues

[Hoover Pilot]

Thank you for your input (and I did know that standard is 1013.2 just couldn't be bothered to type it - I was asking when you change not what you change to!)

I have done a bit of digging and the only paperwork referring to ICAO I have (which is several years old) says that we should go to standard AT transition.

However, the UK seems to have a notified difference in that MATS part I says "When an aircraft has been cleared to climb from an altitude to a flight level vertical position will be reported in terms of flight level unless intermediate altitude reports have been specifically requested by ATC"

This seems that at least one altimeter must be set to standard immeadiately when cleared to a flight level.

HP

[Captain Airclues]

Hoover Pilot

Sorry to deviate from your original question.

In my present airline we set standard when cleared to a Flight Level, and are above 3000ft (our highest Aa). We leave the standby altimeter on QNH until above TA and MSA.

The Flying Manual from my previous company (BA) states;
"When above Acceleration Altitude and cleared above Transition Altitude both pilots set STD on their respective PFD altimeters and cross check each other's altimeter. 1013.2 is set on the standby altimeter when above MSA and Transition Altitude".

I believe that the ATC radar screen automatically adjusts the level/altitude on the screen whatever is set on the altimeter, but perhaps one of our ATCO colleagues could confirm this.

Airclues

[BOAC]

Hoover - the note was not aimed at you!

I believe this question of 'stopping at an altitude' has been aired on pprune before (this forum or 'tech'), and ATC are/should be aware of procedures and should only ask for it if there has been an up-cock after clearing you to a level. You will always have the standby, as Cpt A says, for a reasonably accurate level-off if it is a 'panic' while the main is reset (how's your scan?):D

Looking at the ISA, at 12000mtrs, the change for 1000m is around 20mb, so I guess that works out at around 160-170ft per mb, so I should correct my post to read 'about 33ft' - but as the actress said, who cares about the odd foot. :D ICAO rules?

[buttline]

Sometimes, you have to set 1013 way before TA..

For example, some of our SIDs have FL060 as the level off. Taking off on a day when the QNH is 973mb (as it was a couple of weeks ago) means there is more than a 1000ft difference!!

At high rates of climb during take off the aircraft will go into Altitude Acquire approx 1500ft before the level off!

Setting 1013 at the TA of 5000ft would definitely cause a level bust. Setting 1013 1000ft below the TA (i.e. 4000ft) would probably just about be the last point you'd want to set it in this situation..

[ynot704]

Our company states that we can go straight to 1013(.2) as soon as aircraft is in clean config if cleared to FL. Sby altimeter always has local QNH of departing airfield and then QNH of en-route airfields followed by destination airfield.

[PPRuNe Radar]

Transponders will always send ATC radars the aircrafts level (via Mode C) referenced to 1013.2HPa (MBs are soooo out of date :O ).

However, some ATC facilities have the ability to input the QNH to the radar system and the radar system processors then calculate the aircrafts altitude and display this when the aircraft is below the Transition Altitude (or thereabouts).

[OPEN DES]

there is a lot of debate on this issue. what i have understood from the official documents, you re supposed to change AT transition. however there is one exception and that is when you`re cleared apch above TL, in this case QNH may be set instantly. for me personally it makes most sense to have the PF set standard/QNH on the moment you´re cleared to FL/altitude respectively, to ensure proper level off. with the PNF with the other setting to report alt/FL when required. although i dont particularly like the idea of not synchronizing the altimeters.

S

[paulo]

I've been wondering this one. I fly for fun, but keeping a bit of time between me (spinning say) and the ground sometimes means a good 4 or 5 thou. I've always flown it on QNH with a bit of "one for the pot" chucked in to keep clear of any CAS above defined at FLs.

What's the rule, if you're not blasting through the transition (layer?) at the kind of rate your 3000fpm civvy jet normally is?

[I know, I should get the books out. Just feeling lazy tonight]

[Hoover Pilot]

Once again, thanks for the replies.

It seems to be to follow ICAO protocols one should set standard AT transition - unless in the UK where there is a notified difference and at least one altimeter should be set to standard when cleared to a FL.

If you have a standby altimeter then leaving this on QNH until TA seems to cover all eventualities.

Unfortunately I fly a fleet with a split configuration. One third does not have a standby altimeter so options regarding this are nil. For the two thirds of the fleeet that do have a standby altimeter our company SOPs dictate that it is set to standard AT ALL TIMES so this is pretty useless in the context of this discussion. (How this altimeter is used is another discussion point entirely which I didn't want to get into).

Regards

HP

[5milesbaby]

As a controller I was taught that the standard QNH would be selected when the a/c was cleared to a Flight Level and that then stopping off at an altitude would be thoughtless unless the current QNH was re-iterated

[GlueBall]

Capt Airclues says:I will experiment the next time that I'm at FL370 (not in RVSM of course).

Once level in cruise at 1013/29.92, you can "experiment" with the baro setting without affecting your Mode C and TCAS altitude reporting. It's a "blind" encoder that continuously operates on 1013/29.92 even when your altimeter is set on ONH, or QFE.
:ooh:

5milesbaby: ...when climbing the altimeter is reset to QNE when leaving Transition Altitude, and when descending the altimeter is reset to QNH when leaving Transition Level or "by ATC".
:ooh:

[fireflybob]

Glueball, procedures in the USA may differ but the last time I checked the ICAO/PANOPS stated that on descent QNH would be set as soon as you are cleared to an altitude UNLESS further level flight about the TL is anticipated.

The UK AIP states that QNH will be set as soon as cleared to an altitude unless further Flight Level passing reports are required.

Different operators will define their own procedures in their Ops Manuals (which should of course comply with the ICAO/"states" procedures) and given the luxury of three altimeters on most if not all public transport aircraft this should not be too challenging so long as the crew know what they are doing.

In the UK 1013.25 Mb should be set as soon as the aircraft is cleared to climb to a Flight Level. Takes me back to the days (a long time ago!) when the TA at London Heathrow was 3,000 ft and a departing a/c had a near miss with someone else in the hold cos ATC cleared him to FL 40 and the QNH was around 993 mb so by the time they had set 1013 they were thru the cleared level.

As a result of this incident the TA was put up to 6,000 ft and the UK AIP changed to set 1013 as soon as cleared to a FL. Once you are cleared to a FL then ATC should not stop you off at an altitude other than in emergency but if you've got QNH still set on the standby alt then I cant see this is such a big deal but some pilots seem to think it is!

[PPRuNe Radar]

Glueball

when climbing the altimeter is reset to QNE when leaving Transition Altitude

Not sure why anyone would want to set a QNE in the climb. It is a common misconception that QNE is the Standard Pressure setting. It isn't.

It is the indication which will be shown on your altimeter at a defined aerodrome when 1013.25 is set as your pressure datum.

(ICAO PANS Doc 8400)

[GlueBall]

My Jeppesen Airway Manual, Introduction, Chart Glossary, page 10, defines QNE - "Altimeter setting 29.92 inches of mercury, 1013.2 hectopascals or 1013.2 millibars." During the climb it is set as such upon leaving Transition Altitude.

[Captain Airclues]

GlueBall

You cannot set QNE on an altimeter. As PPR says, it is the reading (in ft or m) that you will get at a particular airfield with the altimeter set to 1013.2HPa.

The reason for not doing the experiment in RVSM was nothing to do with the transponder but I didn't think it wise in busy airspace with 1000ft separation. Did it over Africa, daytime, VMC with the autopilot locked on the other altimeter. The difference between 1013HPa and 1013.2HPa is just over 5ft.

Airclues