Hi, on page 5.60 an example is given for applying PEC to DA. In the example the indicated pressure altitude is 4000 however with the error correction applied the actual pressure altitude is 4002. You say that 2ft would need to be added to the DA however the aircraft is 2 ft higher than the indicated pressure altitude so wouldnt you subtract 2ft from the DA?

Cheers,
Lindsay

I guess it's all in the name. PEC stands for Pressure Error Correction.. So what the chart is telling you is the correction - not the error. Therefore if the correction is +2 it is because the error was -2. If you add 2, you have allowed for that error.

By the way, I noticed a debate going on in pprune about the PEC and + 50ft. Some people have the idea that adding 50ft to the DA is the pressure error correction. However the AIP says that you should either apply PEC to the DA or, alternatively, add 50ft if you do not intend to apply PEC. It is not correct to call the 50ft PEC.

Also, I noticed that in the latest AIP, [AIP DAP 1-1 para 1.5], You should apply temperature error correction because on very cold days the decreased vertical separation between pressure levels in the atmosphere causes altimeters to over read on descent. Temperature error correction would be published in the aircraft manuals.

I looks like all IFR aircraft are going to need two pilots soon!! Or maybe the +50ft option would satisfy the temperature correction as well? It doesn't say anything about that. I'm sure it would not be the subject of an exam question at the moment.

Bob

Thanks for replying I'm still a bit confused though. I'll use your examples on pages 5.60-5.61.

On the example on the chart page 5.60 the altimeter correction is used to get the actual altitude. It says indicated altitude is 4000. 75kts 4000ft the altimeter correction is +2. The example says the actual pressure altitude is 4002. The aircraft is higher than the altimeter reads yet the example says I have to add 2 feet to the DA making me 4ft higher than the approach is designed.

Now with the Perth example page 5.61.
Indicated altitude sea level (0) 100kts altimeter correction -6. So when my altimeter reads 250 my actual presure altitude is 244 (using the same reasoning as the example on page 5.60)
If I subtract 6 from the DA as you say to do I will be making my decision when my altimeter reads 244, however my actual pressure altitude at this point is 238, 12ft less than the approach is designed!

Cheers,
Lindsay