need help to figure this out
 

An aircraft leaves A at 1400, flying at Mach 0.84 (OAT – 58° C). The ETA B is 1436 and the distance between A and B is 300 nm. At what time must a speed adjustment be made if the arrival time is changed to 1438:
A) 1426.5
B) 1427.5
C) 1428.5
D) 1425.5


correct answer is d ...
i have been able to figure out the true TAS=480 and the planned TAS =500

what to do next...is whats bugging me i tried all the speed and time stuff i knew but its confusing the living daylights outta me

Either its too late for me and I cannot properly read the question or the question itself is incomplete - that depends on the speed adjustment! If the thing decelerates to 1 kts just before 1436 you can delay the arrival indefinetely... I dont get it.

This is one of those stupid, pedantic questions that CAAs think is required if pilots. Just pull the Mach back as soon as you know you need to adjust the arrival time and see how it works out. You will NEVER have to do this in real life.

GF

as far i know mach 0.01 difference is 45 sec a hour about. but i don't get the question!

Yes, when assigned a time to cross the oceanic transition point, adjust the speed so that the FMS estimated time over waypoint matches!

I think you guys are right. The speed increment was not provided in the question.

Ah, PROGRESS, page 3, RTA (Required Time At) in the 1R, check the RTA speed in the 2L is reasonable, back to drinking coffee.

It would provide another side of the triangle if they told you what the speed adjustment was in kts.

Reminds me of the old plotting question, "At what time and what position would you need to leave your existing track from A to B in order to arrive over your Diversion field, C, at the same time as you would have arrived over your original destination B. 30 marks! (GS of moving base etc.). So useful to me at the time, flying the BN2 Islander!:)

only thing i know is that you are reducing to about .81. :\

Hi shabez,
I think you'll find the ground speed was 500 kts.

You are missing the new Mach No. they will reduce to - else it's impossible.

Don't you just radio ahead and declare a fuel emergency? :}

It a slightly practical question as sometimes one has to cross
a point at a certain time for ATC separation.

Of course the earlier the better. If left it too late one may be
waaay back on speed to make any real difference timewise.

I'd say what the bugger is asking you, is do you realise the
earlier the better out of the four answers provided? Just my
hunch.