Can anyone enlighten me why there is a quite noticeable fuel odor in the entire cabin when you start the APU with the ECS in the HEAT position?
I'm aware of RFM Part I 2-23. Would just like to know the reason for it.
When you refer to Part 1 2-23 I assume you are referring to starting the APU with the cabin and cockpit heat off. This note refers more to the prevention of robbing bleed air from the APU during its start than to anything else. The Air Source Heat/Start switch should be in the APU position as well. AS to the vapours, I have never experienced much in the way of odor in any of the starts I did, but then again I never started with the heat ON. If one were to guess, then I would say that the bleed air that is used to heat the cockpit and cabin is being sourced from the APU meaning that the Air Source switch is either in the wrong position or is letting bleed air from the APU get by it. The bleed air would be air drawn in from around the APU and it sits just aft and between two other smelly power units, so the air is not going to be fresh initially.
Not sure if I have answered anything, but my 2cents!