Fumes question
 

Hey there,
I have been reviewing the fumes(smoke) checklist for my recurrent.
It talks about orange peel smell being the rain repellant and warns you this may be toxic.
It then says that a smell of pine needles would not be toxic. Got me thinking what the culprit for that would be?

Probably one of those fir tree shaped thingies hanging from the overhead on a piece of string. Big favourite with smokers in an attempt to fool people that their cars don't smell like full ash trays.

I've done some digging. This is pieced together from scraps of info and old patent documents from Boeing, a couple of incident reports and googling so is definitely subject to correction. Perhaps an engineer can step in with a better informed post!

The two smells seem to be the chemical additives used to help us pilots detect a leak:

Orange peel = D-Limonene
Pine Needles = Methyl salicylate

Connecting the dots it would seem that the toxic rain repellent (do we still use Rainboe??) uses D-limonene, and some of the more recently developed non toxic repellents use methyl salicylate.

Therefore when the manuals differentiate between the toxic vs non-toxic smell, I believe they're saying it depends on which aircraft, therefore you'll have one OR the other.

A fantastic answer. Thank you very much. I would have never guessed that they add a substance so we can detect whether it's poisonous or not. Makes perfect sense though.

Recently the question of the original post puzzled me as well.

I found the explanation in this post plausible however it surprised me that this comes also back in the smoke/fumes checklist of the Airbus A400M as this aircraft does not have any rain repellant.

Makes wonder what the explanation would be ?