Brown wings are an honour bestowed to a good chap who has had anal sex with a female (human).
Brown wings have an 'expiry time' of twelve months and are revoked after that period unless you keep up your 'air-time'. This constitutes at least one trip up bourneville boulevard from the initial date that you joined the Brown Squadron. Failure to do so will see you grounded,and no airman wishes that upon himself. Sticking your finger up her bum does not qualify you as a holder of brown wings, you will only be ranked as air cadet for this particular feat.