just want to make sure I understand it correctly ;)No problem at all, Martin. RC is programmed to take the QNH and Transition Altitude at the departure and destination aerodromes and apply this information to a look-up table to calculate the appropriate Transition Level.Here's an extract from an actual RC log of the calculation made with a QNH of 1013 hPa:departure pressure = 29.91778 transition altitude is 4000 transition level is 60 arrival pressure = 29.91778 transition altitude is 4000 transition level is 60 You'll see that the calculation is not done in hPa but in/hg - whether this is just the way jd has written his code or because that's the format in which fsuipc passes the data, I don't know, but that's how it' done. In the example above, RC calculates that the correct TL for a TA of 4000ft is FL60. On your flight, with that QNH and a TA of 11,000ft, RC would have set a TL of FL130. Now, if you remember I said that the "altimeter check" wav was programmed to play as you passed 300ft below the actual altitude of the Transition Level. With a QNH of 1013, FL130 would have been at an altitude of 13,000ft so, on passing 12,700ft, the routine would be triggered and, allowing for a slight delay in the wav playing and your rate of descent, you would have heard it at about 12,500ft (FL125) which is exactly what happened.So, I hope that makes it clear that RC is working correctly in this area; what I'm concerned about is why you weren't given the QNH when you were given descent below the TL but, with luck, the log you sent to jd should give the answer.Pete

Thanks Pete, it's finally all clear now :):)JD replied already and is investigating it.Martin

The last few flights I've got into a lot of trouble with ATC for not maintaining the correct altitude. For example today approaching EGJJ I was at 6000ft (as cleared) with the correct QNH (given to ne by Radar contact)on ALT HLD (PMDG 737) and I was continually told to check my altitude. My altitude was exactly 6000ft. If this goes on I'm afraid I'll lose my licence!!Any ideas anyone please?Peter

Any ideas anyone please?Yes, Peter, as always with these problems, the cause is a mis-set altimeter.The Transition Altitude at Jersey (both real-world and RC) is 3000ft. This means that you would have been cleared to FL60 and not altitude 6000ft which means you should still have had the standard pressure of 1013.2mB set on your altimeter and not the QNH.If the QNH was significantly different from 1013.2mB, this would cause enough of a vertical difference between FL60 and 6000ft to set off RC's altitude "watchdog".Pete

PeteMany thanks for the reply.Peter