FMC entries for European operations

[PeteP 2]

A question from a member of the Radar Contact beta team about operating the 737NG in Europe led me to page 45 of the FMC manual and the section on entering the Transition Level on the Descent Forcasts page.The example shows (at L1) a "Trans Lvl" of 18000. Now as, by definition, the Transition Level is expressed as a flight level, and flight levels are expressed in 'hundreds of feet', this, logically, would be FL18000 which, depending on the QNH, would give an altitude of roughly 1,800,000ft! Not very likely :D so it must be an altitude of 18,000ft. But why require an entry in altitude format when the value is expressed as a flight level? Should this entry not be in FL format? If it is required to be in altitude format, what altitude should be input? Perhaps an example will make things clearer.You're inbound to Heathrow (the QNH is 990mB/hPa) and you ask the controller for the Transition Level. After he's picked himself up off the floor - no one ever asks for the TL! - he scrabbles around in the electronic information system and a couple of minutes later, tells you it's FL65. If you simply add two zeros to this figure and input an altitude of 6500ft at L1, with the current QNH that'll be a FL equivalent of approximately FL72 which, as we've just established, is not the Transition Level.To get it right, the only way seems to be to do the mental arithmetic and work out the altitude equivalent of FL65 - which with this QNH is about 5,800ft - and enter that figure at L1. It seems a hard way of going about things to me!Now it's entirely possible, even probable, that I've misunderstood how the FMC deals with this entry so perhaps one of the PMGD staff could explain this apparent oddity?Pete Pitman

[PeteP 2]

Ooops - after all that, I put the wrong Transition Level in my post. With a QNH of 990mB the Transition Level should read FL70, inputting 7000 at L1 would give a flight Level equivalent of FL77 and the altitude equivalent of FL70 would be 6,300ft.Sorry for the silly error - must have been the beer I had before Sunday lunch :D - but the principle illustrated remains the same.Pete

[PeteP 2]

Hmmm... 48 hours, 121 views but not a single response. Come on fellas - someone must know how this works.:-hmmm Should it be a FL input or, if not, what altitude should be used?Pete

[bobbyjoh 11]

Pete,Thanks for putting this up on the forum. Your note is correct to change the TL on the PFD those settings in the FMC must be changed. However, I belive that the TL being stated in altitudes not correct, however on some terminal plates they are both stated. For example I am flying out of RJAA and the plates states: Trans Level FL 140 and TRANS ALT 14000 feet. No go figure, like you I thought the TA was calculated.I would like to hear from the PMDG team also on what input is used on the real plane.CheersBob Johnson

[PeteP 2]

Hi Bob,As I'm sure you've guessed, it was your question on the RC list that prompted me to investigate this feature on the FMC. I'm awaiting an answer from the PMDG experts with great interest.Pete

[Guest Ross]

Pete, Are you sure it was just the one beer you had? lol.Transition Altitude at Heathrow and indeed throughout the UK is and has been for as long as I can remember 6000ft.Just to be sure I checked the latest textual data sheet for the Airport (AD 2-EGLL-1-8 (18 Mar 04) LONDON HEATHROW UK AIP) and it confirms that it is indeed 6000ft.I know this doesn't answer your question but I thought I'd give you a ribbing anyway.Incidentally, in 300+ hours of flying on VATSIM, I have never heard a Transition LEVEL being given. In my experience its always given as an ALTITUDE, both Airbus MCDUs and Boeing FMCs take it as an altitude. As far as I believe Transition altitude is given as an altitude and not a flight level so that aircraft are always, in the case of the UK, flying at 6000ft AMSL before the altimiter setting is changed to 1013.4/29.92.

[Guest Fortress]

>Transition Altitude at Heathrow and indeed throughout the UK>is and has been for as long as I can remember 6000ft.>>Just to be sure I checked the latest textual data sheet for>the Airport (AD 2-EGLL-1-8 (18 Mar 04) LONDON HEATHROW UK AIP)>and it confirms that it is indeed 6000ft.TA at EGLL is indeed 6000', however it is incorrect to say this applies throughout the UK. Eg. Cardiff (EGFF) is 4000', Manchester (EGCC) is 5000', Birmingham (EGBB) is 4000', Isle of Man (EGNS) is 3000', Liverpool (EGGP) is 5000',...., and there are many more airports different to Heathrow.Just for info, the next time you're on VATSIM ;-)Cheers,Paulhttp://www.strontiumdog.plus.com/cin.gifwww.bavirtual.co.uk/cin.htm - please give generously!!Officially licenced by British Airways plc for use of name and logo[p]AMD XP2800+ Barton, Gigabyte GA-7NNXP nForce2, 1Gig Crucial PC3200 DDR 400MHz, Gainward 128 MB GF4-4200, SB Audigy, 3 x WD Caviar SE[/p]

[PeteP 2]

Hi Ross,You're absolutely right - the Transition Altitude at Heathrow is, indeed, 6000ft and this is a fixed value regardless of the pressure. However, if you look back at my original message, you'll see that it I was referring to the Transition Level - a very different animal - which does vary with the pressure as I illustrated in the example I quoted in my post - albeit with incorrect figures to start with (I really must stop drinking while I'm posting). ;)RegardsPete

[Guest Ross]

Hi Pete,Sorry for generalising with the Transition Alt in the UK. As a rule of thumb it is 6000ft although there are some exceptions.I'll quote your original post: "You're inbound to Heathrow (the QNH is 990mB/hPa) and you ask the controller for the Transition Level. After he's picked himself up off the floor - no one ever asks for the TL! - he scrabbles around in the electronic information system and a couple of minutes later, tells you it's FL65. If you simply add two zeros to this figure and input an altitude of 6500ft at L1, with the current QNH that'll be a FL equivalent of approximately FL72 which, as we've just established, is not the Transition Level."I understand what you're saying about the Transition Level being affected by barometric pressure but the bit that loses me is why the controller would quote you a Transition level of FL65. What I understand from it is that (here goes):Transition Level= Transition Altitude + or - the difference in indicated altitude caused by the pressure deviation above or below 1013Millibars/29.92in divided by 100.Example: Transition altitude is 6000ft, difference in indicated altitude at 1013.4MB and present field altimiter setting is +240ft. Therefore Transition Level= 6000ft+240ft/100= 62.4 = FL62Am I completely off the beaten track here or is this correct. As far as I understood it before Trans Lev was just Trans Alt minus two zeros although I appreciate that these two values are only the same when at standard altimiter setting.

[Guest Ross]

Hi Pete,Sorry for generalising with the Transition Alt in the UK. As a rule of thumb it is 6000ft although there are some exceptions.I'll quote your original post: "You're inbound to Heathrow (the QNH is 990mB/hPa) and you ask the controller for the Transition Level. After he's picked himself up off the floor - no one ever asks for the TL! - he scrabbles around in the electronic information system and a couple of minutes later, tells you it's FL65. If you simply add two zeros to this figure and input an altitude of 6500ft at L1, with the current QNH that'll be a FL equivalent of approximately FL72 which, as we've just established, is not the Transition Level."I understand what you're saying about the Transition Level being affected by barometric pressure but the bit that loses me is why the controller would quote you a Transition level of FL65. What I understand from it is that (here goes):Transition Level= Transition Altitude + or - the difference in indicated altitude caused by the pressure deviation above or below 1013Millibars/29.92in divided by 100.Example: Transition altitude is 6000ft, difference in indicated altitude at 1013.4MB and present field altimiter setting is +240ft. Therefore Transition Level= 6000ft+240ft/100= 62.4 = FL62Am I completely off the beaten track here or is this correct. As far as I understood it before, Trans Lev was just Trans Alt minus two zeros although I appreciate that these two values are only the same when at standard altimiter setting.

[Guest nutcase]

look at this: http://home.online.no/%7Eeisoere/VACCN/Refsheets/TA_TL.htmlso in your example with TA= 6000 at 1013.4QNH will give a TL at FL075.http://home.online.no/~roa-sand/artcc/train/tatl1.jpgJan Roar R

[PeteP 2]

Ross,It was someone else who mentioned the various Transition Altitudes in the UK, not me but he is correct. The standard UK Transition Altitude is actually 3000ft.As far as the Transition Level is concerned, definitions vary but in the UK, it is defined as the lowest useable flight level above the Transition Altitude. "Useable" flight levels in the UK are at 500ft intervals - FL30, FL35, FL40, FL45, FL50, FL55, FL60, FL65, FL70 and so on. The arithmetic for calculating the TL is very simple. I'm assuming a Transition Altitude of 6000ft, that 1mB=30ft (that's the usual convention for rought calculations of this sort) and a QNH of 990mB that I used in my original example. Take the difference between the standard pressure setting of 1013.2mB (we'll ignore the .2 for the purposes of this exercise) and the QNH of 990mb (1013-990=23) and multiply by 30ft to give the vertical distance between Transition Altitude and the Transition Level - in this case 23x30=690ft. Rounding this up to 700ft for ease of calculation gives us 6700ft (6000ft TA + 700ft) above the 1013.2mB pressure line i.e.FL67.FL67 is not, by definition, a "useable" flight level in the UK so we round up to the nearest 500ft interval to give FL70 as our Transition Level. In practice, this calculation done by using a look-up table similar to the one Jan provided the URL for (but with different values). I used the UK table to establish the TL in my original post but, stupidly, misread it as FL65.This is all rather academic, though, because for IFR airways traffic, we don't use the Transition Level but another value known as Minimum Stack Level (Min Stack) which ensures that there is always at least 1000ft between aircraft operating at the Transition Altitude and those flying at the lowest flight level. In the example I've just given (TA 6000ft, QNH 990mB) Min Stack would be FL80.Pete

[bobbyjoh 11]

Guys, This is why this forum is so good. I am learning a lot with this discussion. Now with controllers and real pilots putting there two cents into this, we can all learn a lot.Thanks Pete and everyone else adding to this discussion, Can we keep this going, this really is good stuff.Bob

[PeteP 2]

Bob, As you know from the RC Beta Team's list, I'm happy to talk about altimetry until the cows come home but what I'd really like is an answer to my original question - is the requirement to input the Transition Level in an altitude format an error and, if not, what altitude should be used? I know it's hardly the most important - or interesting - subject they've ever had on the forum but it would be nice to get some sort of response from the PMDG team.Pete

[Guest pagotan]

Hi Pete,All Boeing FMCs I have had to deal with sofar read altitude entries in feet or flight level. The FMC makes use of your entry to display the altitude in the correct format ie. altitude or FL based on the aircraft position and the transition level of the country. In the UK an altitude entry of 6000 will be displayed as FL060 but in the US an altitude of 8000 will be displayed as 8000.As to the Descent forecast page the TRANS LVL defaults to FL 180. Manual changes are permitted in either format.Having said that there may be some programming constraints that prevented the PMDG developers to reproduce accurately the genuine FMC logic. I fully agree with you that PMDG should comment on this issue and give some guidance on how to handle it. It may be so that these calculations are not implemented at all in the sim or that country specific transition levels are not recognized.DISCLAIMER:The above reflects only a personal opinion and was written without any intend to offend, harm or criticize in any way or manner any individual, institution, association or company including PMDG.Michael