Hi Bob and Richard,

Just a maths question re interpolation

1) You may have come across this before in exercise 4 of exercise 4.17 in regard to the interpolation technique - In the above question I can see exactly why you have you used both the 17500 feet as well as the -10 deg OAT since both require some degree of interpolation, so interpolation is used on three elements, altitude (17500 ft), weight (2250kg) , and OAT temperature (-10 deg c which equals +10 ISA) or, not just one in isolation.

From a maths perspective, should I simply add ALL of the eight interpolated figures and divide by 8 (the total number of variables to be interpolated between), or should I add the figures in each section or column and then divide by 2 or 4 respectively and THEN add together and divide at the end. Which way is most accurate?

I might just be over-thinking this (quite possible) and most of my answer seem to come somewhere close but I just want to make sure I have my technique correct for the purpose of examination.

And just one other probably easy fuel question - startup and taxi allowance fuel is only based on the takeoff aerodrome is it not, rather than including taxi after landing as well?

Any help appreciated!

Brook

Hi Brook,

Both ways will give you the same answer (unless you do a lot of rounding in the intermediate steps of your second approach) but the former is much less work. Therefore, if interpolating multiple values just add them all together and divide by the number of values to get the average.

Taxi/start-up allowance is only included once in your fuel calculations and typically won't include any taxi requirement for your destination. After all, after you have landed, the flight is over and you would still have the fixed reserve in the tanks - you'd just use that to get to the ramp if you needed it Your school or the examiner will specify if they require a destination taxi allowance but that's not likely to happen.

Cheers,

Rich

Thanks Richard - that's great.

I figured that MIGHT be the case but just wanted to make sure so adding them ALL up (within different columns and rows) and then dividing by the total number is fine .

Its the English language at times as well - re the taxi allowance - It could be one of those really big airports with several KM of runway and taxiways...but I will revert to the school or examiner in that case!

Brook