Fumes question

[applecrumble]

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?

[ericferret]

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.

[Kerosine]

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.

[applecrumble]

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.

[FKO]

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 ?