Seriously, not a good time.
Airlife has just gone tits-up, which means some very well regarded and established authors (Trevor Thom, Brian Cosgrove, etc.) are up for grabs and the existing aviation publishers are getting them. Although these chaps are suffering not much more than a bit of short term stress, it does rather mean that the specialist publishers existing "new product" budgets are rather eaten up.
This really means that unless your friend is an aviation household name (and presumably John Farley would have posted the question in his own name
or called in a few favours) he's in the mill of trying to persuade mainstream publishers to take it - and that's very very hard.
She doesn't read this forum but if you want some advice on what is cruelly but not entirely inaccurately known as vanity Publishing you might drop a PM to Whirlybird, who published her own book of Guinness-record-breaking-exploits privately, she may have some useful advice to offer. (If you don't know the good lady, she's often found hanging around in Rotorheads, Jet-Blast or Private Flying). (And a very readable book it is too, I recommend it).
G
(First book coming out later this year, not under the name Genghis, but not self financed either - I'll leave you chaps and chapesses who don't know me personally to guess which is mine when it appears in the Christmas pilot-shop catalogues.)
N.B. There are two books, you can usually get them in mainstream bookshops such as WH Smiths called "The Writers Handbook", and the "Freelance Photographers Market Handbook" which are invaluable to those of us who supplement our income through the written word and occasional photograph. The former at-least might be worth an investment.