Instrumentation dilemma

[Martin1234]

It seems that I know what errors EAS, CAS, TAS, MACH and IAS takes into account.

The problem starts when I need to answer a question like "if you climb with a constant CAS, what happens to the TAS" etc.

Is there any "rule of thumb" or an explanation that would help me when faced with questions like the aforementioned?

Also, are you allowed to use a calculator and a flight computer during the test (UK)?

Thanks.

[Polarhero]

The little way i remember is....

+MTC-

just pick what you want to be constant then look above and the sign to the side tells you what happens..

So if climbing at constant CAS, TAS goes up and Mach goes up more. Or if climbing at constant Mach TAS goes down and CAS goes down more..

that works for climbing

In the decent use

+CTM- in the same way, so decending at consant Mach, TAS goes up and Cas goes up more.

Hope it helps.

[cadaha]

Just been reading about that in course manuals.

General rule of thumb. In a steady climb CAS/RAS (calibrated air speed/Rectified airspeed) or IAS (indicated airspeed) will be less than the TAS (True airspeed) due to the density of the atmosphere being less at altitude. The higher you go the bigger the difference. Don't forget that variables will change this difference such as air temp and pressure etc.

For instance using ISA Settings of temp = +15 and MSL pressure = 1013.25 as a base. You can work out the difference between IAS and TAS.

Even at zero altitude there can be a difference such as:

If the temp and pressure are as per ISA then IAS will equal TAS
i.e. IAS = 80 / TAS = 80

if the temp is 45 degrees (ISA + 30) then TAS will be greater than IAS i.e. IAS = 80 / TAS = 87

Just set yourself some examples and try them out on the whizz wheel and you see the differences. (And it will be quicker than trying to work them out on paper).

[pipergirl]

I found using the ERTM graphs helped me and were very straight forward...
if you follow this link, and scroll down a few posts, you'll see that someone has posted the graphs fully in different conditions ie ISA, isothermal layer, inversion..

http://jals.co.uk/forum/showthread.php?t=2150

hopefully that will help you out:}

andyou can bring a calculator(a non-programmable one) and a flight computer in with you