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When both propellers of the aircraft reach the time limit (60 month) and need to be replaced, can both propellers be replaced at the same time and perform only one flight test to reduce time on ground or should they be replaced one at a time just for safety or to investigate any discrepancy that may arise?

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    $\begingroup$ It's a useful idea to include a details on the country and legislation, since these can change from area to area and helps to narrow the down possible answers for the type of aircraft you are interested in :) $\endgroup$ – Thunderstrike Jun 8 '15 at 9:42
  • $\begingroup$ I can't name a source now since it is quite a while since I've seen it, but I believe to remember that at least in the EU and Switzerland this does not work. Testing a propeller implies a high probability of it failing thus you need the other one to already be tested to ensure that at least one is most likely working with no problems. Therefore you would have to replace one, test it, then replace the other one and test it. If I can find the source again, I make it a full scale answer, till then I hope somebody else can point you in the right direction. $\endgroup$ – Patric Hartmann Jun 8 '15 at 10:14
  • $\begingroup$ Why is a flight test needed for a prop change? $\endgroup$ – Steve H Oct 22 '15 at 23:46
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    $\begingroup$ @SteveH That sounds like an interesting thing to ask as a new question. :) $\endgroup$ – reirab Oct 23 '15 at 4:32
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    $\begingroup$ Any paralells to a brand new plane with two untested props? It is probably flight tested at only one test event. $\endgroup$ – Wirewrap Nov 10 '15 at 22:34
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Since replacing a propeller with the same propeller that is in the Type Certificate is not a major repair, the FAR(s) (CFR Title 14) that most apply are 43.7 and (assuming the airplane is under Part 91) 91.407.

43.7 states:

(a) Each person performing maintenance, alteration, or preventive maintenance on an aircraft, engine, propeller, or appliance shall use the methods, techniques, and practices prescribed in the current manufacturer's maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer, or other methods, techniques, and practices acceptable to the Administrator, except as noted in §43.16. He shall use the tools, equipment, and test apparatus necessary to assure completion of the work in accordance with accepted industry practices. If special equipment or test apparatus is recommended by the manufacturer involved, he must use that equipment or apparatus or its equivalent acceptable to the Administrator.

(b) Each person maintaining or altering, or performing preventive maintenance, shall do that work in such a manner and use materials of such a quality, that the condition of the aircraft, airframe, aircraft engine, propeller, or appliance worked on will be at least equal to its original or properly altered condition (with regard to aerodynamic function, structural strength, resistance to vibration and deterioration, and other qualities affecting airworthiness).

So you must follow the maintenance manual and put the airplane back in a state at least as good as original. If you think that putting them both on does not qualify to satisfy this requirement, then you should do them one at a time. If it does satisfy this, then in that case, 91.407 comes into play, which states:

(a) No person may operate any aircraft that has undergone maintenance, preventive maintenance, rebuilding, or alteration unless—

(1) It has been approved for return to service by a person authorized under §43.7 of this chapter; and

(2) The maintenance record entry required by §43.9 or §43.11, as applicable, of this chapter has been made.

(b) No person may carry any person (other than crewmembers) in an aircraft that has been maintained, rebuilt, or altered in a manner that may have appreciably changed its flight characteristics or substantially affected its operation in flight until an appropriately rated pilot with at least a private pilot certificate flies the aircraft, makes an operational check of the maintenance performed or alteration made, and logs the flight in the aircraft records.

(c) The aircraft does not have to be flown as required by paragraph (b) of this section if, prior to flight, ground tests, inspection, or both show conclusively that the maintenance, preventive maintenance, rebuilding, or alteration has not appreciably changed the flight characteristics or substantially affected the flight operation of the aircraft.

I would argue that a propeller change cannot be satisfied by (c) above and does require a flight test. However, there is nothing that requires separate flight tests UNLESS the maintenance manual requires it, in which case part 43.7(a) from above comes into play. But as a "fail safe" a good run-up on the ground at high throttle with the brakes applied, followed by an inspection of the work can give good confidence in the work prior to the flight test.

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    $\begingroup$ Welcome, nice answer for a new guy, well done! The only thing you're missing is a source reference, and a good link to the source. Thanks for finding an old question in desperate need of a decent answer. $\endgroup$ – FreeMan Jan 25 '16 at 21:01
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    $\begingroup$ Sure thing. FARs are the Federal Aviation Regulations, which are in CFR (Code of Federal Regulations) Title 14. Pretty much any websearch will give them, I linked to one of them. $\endgroup$ – Paul Jan 25 '16 at 23:24
  • $\begingroup$ @Paul, Truly a quality answer! Welcome to Aviation.SE! $\endgroup$ – J Walters Jan 26 '16 at 2:36
  • $\begingroup$ Excellent, @Paul, well done! That now nicely fits the StackExchange model, and should garner you more up votes. Since your first answer was this good, I'm certain you'll grace us with many other excellent answers, as well. $\endgroup$ – FreeMan Jan 26 '16 at 13:05
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It would probably be safer to replace one at a time in case the propellers were defective. Better safe on one good prop than sorry on two bad ones.

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    $\begingroup$ Just because you say so? Or are there any requirements to do so? $\endgroup$ – CGCampbell Nov 10 '15 at 20:42
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    $\begingroup$ Check your country's rules on that, but even then it is one of the unwritten rules of flying that keeps almost everything with a fail-safe backup. $\endgroup$ – SMS von der Tann Nov 10 '15 at 20:47

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