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The reason I ask this question is because I am a programmer and developing ETL processes to calculate reliability of products that are installed in aircrafts.

I have been getting A lot of bad data from the OEMs.

I have been told by an engineer at my organization that the maximum number of flight hours an aircraft can have is 400 hrs a month.

Is this accurate per FAA regulations?

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    $\begingroup$ As a programmer I would tell you to build your model on the assumption that the maximum number of flight hours an aircraft can accumulate in a month is 745: Flying 24 hours a day for 31 days (the most you can have in a month), plus one hour - "What if the plane is Air Force One & refuels mid-air for a month without landing?" This particular edge case is highly unlikely - it may even be impossible (I don't know how long a VC-25 can fly without any maintenance) - but why not handle it? $\endgroup$ – voretaq7 Mar 6 '15 at 6:57
  • $\begingroup$ So you're a data analyst, not an embedded systems engineer, so I guess it's not as big of an issue, but Stack Exchange probably isn't the right place to get your system's requirements, is it? If you were an embedded systems engineer, it would be downright irresponsible. Anyway, there's nothing in the FARs that limits flight time "by month". There are however air worthiness regs (maintenance basically) that must be complied with. These are going to vary based on the category of plane. faa.gov/aircraft/air_cert/airworthiness_certification/… $\endgroup$ – Calphool Mar 6 '15 at 16:55
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    $\begingroup$ @Calphool I am not a data analyst. The ETL process is only one component of implementation. I am a solutions developer and developing a reliability management system. Why so gung ho on the judgment? Nor am I getting requirements here. I was skeptical about flight hour data and thought one's with aviation experience might provide some insight. $\endgroup$ – Squ1rr3lz Mar 6 '15 at 17:29
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    $\begingroup$ @Calphool - I don't see a problem with seeking guidance here, especially for a non-critical component of his software. If it were true that there was a hard limit of 400 hours imposed by the FAA, he could code a warning in the ETL that the numbers appear to be out of range. If software engineers never used StackExchange for guidance, my company's developers would be a lot less productive :) $\endgroup$ – Johnny Mar 6 '15 at 18:29
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I don't think there is any regulation on max flying hours, just regulations on maintenance intervals.

The "A" check is the most frequent check, and according to Wikipedia:

This is performed approximately every 125 flight hours or 200–400 cycles. It needs about 20–50 man-hours and is usually performed overnight at an airport gate or hangar. The actual occurrence of this check varies by aircraft type, the cycle count (takeoff and landing is considered an aircraft "cycle"), or the number of hours flown since the last check. The occurrence can be delayed by the airline if certain predetermined conditions are met.

The other checks include:

  • B check - every 4–6 months, requiring about 150 man-hours and is usually performed within 1–3 days at an airport hangar

  • C check - every 20–24 months, requiring about 6000 man-hours, taking 1 to 2 weeks to complete

  • D check - major maintenance check, occuring about every 6 years, requiring 50,000 man hours, generally spanning a couple months.

Note that all of these times are approximate, depending on the exact maintenance plan filed by the airline and the aircraft type. Also cycle count may be factored into the maintenance intervals in addition to flight hours so aircraft that do many short-haul flights may have more frequent maintenance.

So in any case, only looking at the A checks, if you can land, refuel, service, and get back in the air in 2 hours between 10 hour flights, the plane could stay in the air for 20 hours/day. Every 6 days, it will need some downtime for the A checks, let's say the airline puts enough people on it to get the check done in 5 hours. So that's 125 hours per cycle: 120 hours flying, 5 hours in maintenance. They can fit 4.83 of these cycles in a 30 day month so the aircraft could be flying up to 580 hours in any given month (but that last A check gets deferred to the next month, so that means less time in the air that month.

With longer flights (which reduces the overhead from turnaround times) and tighter turnaround times, the flight hours per month could be higher. If you really want the maximum for a month, then if you assume 125 hours per maintenance inverval and that the plane is kept in the air as long as possible with 0 turnaround time, that's around 690 flying hours out of 720 total hours in a month.

Of course, this makes a big assumption that the A check interval really is 120 hours, and that the time to do the maintenance is 5 hours, in the real world both numbers will vary based on aircraft, airline, and maintenance staffing levels.

Plus, over the longer term, you need to factor the other, less frequent but also more time consuming maintenance checks (B through D checks), as well as allow downtime for unexpected repairs.

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  • $\begingroup$ Thank you for response...I am aware of the maintenance intervals...580 seems right...I wanted to take these intervals into consideration...you provided an awesome answer...+1 and answer accepted. $\endgroup$ – Squ1rr3lz Mar 6 '15 at 6:22
  • $\begingroup$ @user216392 Is there B Checks as well? $\endgroup$ – Squ1rr3lz Mar 6 '15 at 6:23
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    $\begingroup$ Yes, checks range from A - D with A being the most frequent (but fastest to complete, it's generally completed overnight) and D being the least frequent (every 6 years or so) but consuming the most time with around 50,000 man hours and 2 months real time being required for the check. $\endgroup$ – Johnny Mar 6 '15 at 6:43

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