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## daylight hours and transititon layer

• Flyz
• Topic Author

### Flyz created the topic: daylight hours and transititon layer

Hey Guys

just a few questions on nav

1) can someone please explain how to work out the thickness of the transition layer when say the QHN is 1001 hPa

2) when working out daylight hours, do we have to take into account the flight time?
I can work out the BOD and EOD and get the daylight hours, but a flight traveling east or west, what do you do then?

cheers

• Posts: 1914

### bobtait replied the topic: daylight hours and transititon layer

The hours of daylight available are not at all affected by the flight you intend to do. BOD at the departure aerodrome and EOD at the destination will occur at a particular time whether you fly or not. You must remember however, to bring both of those times to the same name [usually UTC], before you attempt to subtract BOD from EOD. Also make sure you always write the times as SIX figure groups.

The simplest way to calculate the thickness of the transition layer is to covert the transition altitude [always 10,000 ft on QNH], to a pressure height using the following formula. 1013 - QNH x 30 + 10,000. The transition level varies with the QNH according to the diagram on AIP ENR 1.7 Page 5. Because all flight levels are also pressure heights, you can then subtract the figure you obtained when you converted the transition altitude to a pressure height from the transition level applicable to the given QNH.