Speed/Distance/Time/HELP!

[BigHeadNuts]

Hi,
I have my second stage interview for NATS soon, and i am doing all the usual preparation. However, im stuck with S/D/T calculations, such as how to work out questions like "if an aircraft runs out of fuel 60 miles from an airport while at 20,000 feet, glides at 240 knots, descending at 2000 feet per minute - will it make it to the airport?"

I am familiar with the SDT triangle, but i think it is a bit more complex than that! Any help would be great,

Thanks all.

[britkit]

Okay, I'm not perfect at these things and I'm sure someone wil put us both right if I get it totally wrong but here goes:

In the example you give the aircraft is at 20,000ft losing 2000ft per min - so you've got 10 minutes (20,000 divided by 2000) to get it on the deck before gravity does the job for you.

You also say the aircraft has 60 miles to run to the nearest airport and is gliding at a speed of 240kts (fast - that's 4nm a minute (60 x 4)) - so

4's into 60 go:- 15 times i.e. 15 minutes, so the aircraft WOULD make it to the airport 60 miles away with a little room to spare.

Britkit:ok:

[SirToppamHat]

I think you're wrong britkit, but our posts crossed.

Just take it in stages.

60NM at 240 Knots = 15 mins

15 x 2000ft =30,000ft

The ac will arrive at the airport 10,000ft BELOW the threshold, so the answer is no, it will not make it.

Actually, it will crash 20NM short of the airport.

There are lots of threads on here that have addressed these sorts of problems. The ones people usually struggle with are those that require two separate calculations to be 'merged'. For example:

An aircraft is heading east at 275 knots, and another is heading west at 325 knots they start 75 miles apart, how long before they hit?

Again, it is quite simple:

CLOSING SPEED is 325+275 = 600 knots

600/60(minutes) =10 NM per minute.

75/10 = 7.5 minutes to impact.

There are other threads, try a search on speed distance and time.

Good Luck

STH

[aluminium persuader]

STH is right.

Britkit - so were you, right up until the last line. He's got 10 mins in the air but the field is 15 mins away. Oops!

ap :{

[Inverted81]

easier way to think of it
20000ft divided by 2000fpm = 10 mins before it hits the deck

at 240 kts its travelling at 4miles per min so

10mins x 4miles permin = 40 miles

therefore as said above 60-40=20
so will hit the deck 20 miles b4 touchdown unless descent profile is changed.

i find this a much more logical way to work out. see whats best for you!

:E :sad: :ok:

EDIT: just read an earlier post... seem to have posted the same solution ooops (sorry chaps) but hopefully my layout may clear things up. i like to keep things as easy as i can!

[foghorn]

The easiest way to think about SDT calculations is to think in miles per minute - basically by knowing your 6 times table - 60 knots = 1 mile per minute, 120 knots = 2 miles per minute, etc.

Then you can work out all sorts of things like distances travelled, how long until a faster aircraft catches a slower aircraft, etc.

This has the double bonus that rates of climb/descent are quoted in feet per minute so you can work out distance to top of climb/drop more easily.

Finally it gives you a good gross error check if you are calculating by hand.

[BigHeadNuts]

Thanks for all you help guys, should stand more of a chance of getting that bit right now.

Appreciate your help, wish me luck :D

BHN

[shgsaint]

Is it good that I worked out he initial example in about 45 seconds?

I've already had a stage 1 interview with NATS about 4 years ago.

Needless to say I never made it past so i'm guessing something else to blame other than my SDT calculations.

Maybe I came up as a psycho on my psychometric tests! :}

[Jerricho]

Mine's pickled and it took me 8 :p

[Gonzo]

Jer, he said seconds. 8 minutes is nothing to boast about! :E

[eastern wiseguy]

Depends if he 's still talking about time and distance!!:E

[Gonzo]

8 minutes still ain't nothin' to boast about, EW! :E