Since it's a slow night on the telly, I found myself irresistibly drawn all the way down this thread, and have been amazed.
Not so much by the sniping between those who think they know and those who think they know better, because that's normal for pprune (and most forums (fora?))....
….but the thread has gone an amazing distance without anyone pointing out the actual frame of reference for what may be deferred and what not (whether it's about valve caps or anything else).
I hasten to point out that this reference is only applicable to those aircraft subject to EC2042/2003 (i.e. aircraft under EASA regulations). Other types of operation may well have similar or different requirements, but the following is good for EC registered aircraft...
M.A.403 Aircraft defects
(a) Any aircraft defect that hazards seriously the flight safety shall be rectified before further flight.
(b) Only the authorised certifying staff, according to points M.A.801(b)1, M.A.801(b)2, M.A.801(c), M.A.801(d) or Annex II (Part-145) can
decide, using M.A.401 maintenance data, whether an aircraft defect hazards seriously the flight safety and therefore decide when and which
rectification action shall be taken before further flight and which defect rectification can be deferred. However, this does not apply when:
1. the approved minimum equipment list as mandated by the competent authority is used by the pilot; or,
2. aircraft defects are defined as being acceptable by the competent authority.
(c) Any aircraft defect that would not hazard seriously the flight safety shall be rectified as soon as practicable, after the date the aircraft defect was first identified and within any limits specified in the maintenance data.
(d) Any defect not rectified before flight shall be recorded in the M.A.305 aircraft maintenance record system or M.A.306 operator's technical log system as applicable.
Once you get your head around this it's very straightforward –
If you have an MEL and it's listed, you can defer it.
If you have an MEL and it's not listed, go to the approved data and check if it should be there.... if so, install it or stay on the ground.
If you don't have an MEL and the Manual says it should be installed – install it or stay on the ground.
Palatialvilla has said the best words on this so far, inasmuch as you may be able to get an NTO from QA to deviate from procedures, after all, your MEL was written by your Company. (Note: MEL, not MMEL).
All this stuff about whether it's a seal or a dust cap isn't worth squit in EASAland, neither is how much judgement is good for the soul – wake up guys & gals, you ain't allowed to use judgement these days, 'cos EASA says so.....
Now, whether you go with what you're actually allowed to do or whether you use that hard-earned judgement is up to you, but at the court of enquiry they won't care whether the rules are sensible or practical, just whether or not you followed them....
...and it's taken me over 40 years to get my head around that bit...... funny old world
