Exeng,
Fair enough.
Regarding how to guess cloud thickness what I do is I obtain a thorough weather briefing and I look at charts and satellite imagery. That gives me an idea. Is it always perfect? Of course not, but by doing it frequently I am able to obtain some good results every now and then.
The APU thing...letīs see. Long taxi routes with frequent stops. 20 to 30 minutes to the gate. Normal Procedure is to start the apu as soon as active rwy vacated. What I do is I tell my first offcers that we are NOT going to do that, but instead we are going to start the APU when joining GOLF (for example). That is a few minutes from the gate just in case. It serves two purposes, economy and ecology. So far no one has felt insulted.
Exceptions to that apu start delay thing that I do...
1. If the aircraft is rather light (around less than 55 tons in a 700, other conditions such as airport elevation, temperature, slope not conspiring) I turn on the apu and shut down one engine, after 2-3 minutes.
2. Extremely hot weather, long taxi, apu comes on, isolation valve closed, left engine bleed air switch off, apu bleed air switch on, for cooling.
If I have time and some minivolts are still energizing my brain, I try to think of those things.....those things in the back, called passengers.
Regards,
SW.