ATPL instruments

[LDG_GEAR _MONITOR]

help if poss !!

reading up on past feedback for instruments exam and carnt find an answer to to get my head round the following.

what is the effect on altimeter/ASI/machmeter when climbing/descending into/out hot or colder air ? or the classic through an inversion ?

any help appriciated !

[Flying_Tuur]

You have to take into account that cold air is denser. Therefor, your altimeter will indicate less then the actual altitude. This can be checked while on e very cold day performing your outermarker check on an ILS, you will read a lower altitude while being perfect on glide. If I remember well, it is a correction of 1%/4°C.

For the speedindicator, I don't know by heart. But, if I think logically, the speed is total p - static p. Because both pressures will be affected by the cold, I don't think there is a correction to be made. (I could be wrong on this one !!!)

Concerning your Mach indicator. The lower your temperature, the lower speed equals mach 1. Thus, for a constant true airspeed, flying into colder air will increase your machnumber.

For hot air, it's all the opposite of course.

I hope my simple explanations are any help to you, it's been a long time since I had to do this stuff.. <img src="wink.gif" border="0">

[Paul Hickley]

If you want help with this or any other JAA-type "Ground School" question, I suggest that you post it on the "Ground School" section of the <a href="http://www.oxfordaviation.net/forum" target="_blank">@SK OXFORD FORUMS</a>,where it will be answered by an experienced instructor.

You don't have to be an Oxford student to use the forum.

Click on the above link or go to <a href="http://www.oxfordaviation.net/forum." target="_blank">http://www.oxfordaviation.net/forum.</a>

All the best,

Paul

[LDG_GEAR _MONITOR]

paul

thanks for the reply but as i read this i set off for my exams starting at 1pm today ! but many thanks and if it goes pete tong again - expect me on the blower for some brush up courses as it willtake me onto the 3rd resits ! dont want to be going that way !