Hi Chip,

The passive uses the auxiliary 'être', just as in English -

est + PP = is 

a été + PP = has been

aura été + PP = will have been

aurait été + PP = would have been 

etc. 

The verb être, using avoir as an auxiliary ( just as avoir does ----> avoir eu )

I hope that helps!

Hi Robin, 

Please take a look at the following lesson on forming a passive voice with simple tenses which uses the verb 'être'  -

Forming La Voix Passive with simple tenses in French (French Passive Voice)

With compound tenses, you conjugate the verb 'être' which takes the auxiliary  'avoir'  as per lesson about its passé composé  -

Conjugate être (+ avoir) in the compound past in French (Le Passé Composé)

I think this might be the reason you think we are using 'avoir' but in fact, it is still the verb 'être' conjugated.

Hope this helps!