help with Performance question

[Chintito]

can someone kindly have a go at explaining whats going on with this question...

A planned landing at an airfield produced the following results:

still air landing weight forecast wind landing weight

RNWY A 57000kg 61000kg
RNWY B 59000kg 57000kg

If the WAT limit is not limiting and the aircraft max landing weight is 62500kg.
The maximum planned landing weight is :

A 62500kg
B 61000kg
C 57000kg
D 59000kg

correct answer given : D


another quick one that im sure is bread and butter but i cant see it

an aircraft iwth mass 11000kg is capable of maintaining a gradient of 2.6%. with all the atmospheric variables remaining teh same, woth what mass would it be able to achieve a gradient of 2.4%?

A 101530kg
B 110000kg
C 119167kg
D 121167kg

correct answer : C

many thanks

[Tinstaafl]

Q1.

This is a problem about 'gotchas' ie you have to plan to cover the worst case but without unnecessarily restricting yourself. Generally, if you've covered the worst case then automatically you're also OK for a better situation. With regard to this question, consider this:

If you planned your landing weight based on an increased LW the forecast wind would allow, what will you do when you arrive overhead if the now required wind isn't as strong as your carefully planned landing weight needs for the available runway length?

So, you have the choice of two forecast winds, the catch is that it's only forecast and you're stuck IF you arrive overhead at that weight but the wind isn't there.

That eliminates the heavier rwy/wind Ldg weight. The lighter one would cover you for all conditions BUT doesn't maximise landing weight.

What's left is nil wind. Again, the lighter weight would cover you but doesn't maximise LW.

In this problem you can use the heavier nil wind weight based on this logic:

If you arrive at 59t and there is no wind you're still OK for Rwy B.

If you arrive at 59t and the wind is as forecast you can't use Rwy B *however* Rwy A now becomes useable at 59t. The wind that is preventing you using Rwy B is the same one that enables Rwy A and 59t doesn't exceed that wind's limitation.



Hope it was obvious I ignored the Max LW, since the runways aren't capable of allowing it.

[OneIn60rule]

It's a simple ratio question. At least I believe that is what it's called. >)

2.6% / 2.4 % = 1.0833333

Now simply multiply 1.08333 with 11000 and you get the answer =11916.66

11000 = 2.6%
X = 2.4%


Here's another one> Weight is 33000 kgs and your gradient is 2.6%. What mass would you achieve with a gradient of 2.9%?