This question involves ‘backwards use’ of the reference lines …

NORMAL use of the REF LINES means you go to the REF LINE … then adjust to the condition.

Backwards use of the REF LINES …. To the CONDITION FIRST, then adjust back to the REF LINE.

So for this question, we need altitude …

Work normally with DISTANCE and WIND, draw a line straight through the ALTITUDE section.

Now work backwards with FUEL and LW … enter at 15000kg, straight across to 50000kg LW condition, now adjust down to the REF LINE. BUT, which curve do we use – we need to know altitude – so guess to start with – use a ‘mid’ line, half way between 37000ft and 10000ft (23000) … this takes me to one grid square above the 14000kg line … now draw a line straight through the altitude section … the 2 lines intersect at 17000ft.

Now we could go back and adjust our LW correction to reflect 17000ft … (we guessed 23000ft) … this would bring it 1˝ grid squares above 14000kg … answer 16500ft?? (but looking at the answers, there isn’t really a need!)

Wasn’t that fun!!!!!! There are a few of these “BACKWARDS” questions in the exam system.