cycle limits

[Craig.]

OK this is something i havent really known and i hope someone here can help.
What are the limits on how many flights a plane can fly before it needs to take a break basically. This is more aimed at the long haul flights, for instance Delta run their 777's boston to LGW back and forth with only 2 or 3 hours max between flights, thats a 7 hour flight its gotta take its toll on the engines and airframe.

[OTTOL]

In addition, GEAE conducted 228 hours of comprehensive engine flight testing of the GE90 on the company's specially modified Boeing 747 flying testbed prior to testing on the Boeing 777. Having completed more than 19,000 cycles before entry into service, the GE90 has undergone even more testing than GE's CF6 and CFM International's CFM56 engines, which have established themselves as the most reliable turbofan engines in commercial aviation.

The GE90 is the only engine in the world to demonstrate the ability to achieve more than 110,000 pounds (489 kN) of static sea level thrust. GE90 development engines have operated at thrust levels in excess of 100,000 pounds (444 kN) for a total of more than 80 hours. One engine operated continuously at more than 100,000 pounds (444 kN) of thrust for 20 hours, and engine hardware was in excellent condition at the end of the test. Based on these outstanding results, GEAE accelerated development of the first GE90 growth engine, the GE90-92B.

The only real limiting factor is Fuel and crew fatigue. Once the airplane is airborne, the amount of stress on the airframe and engine components does not increase. I tried to search online and find the exact numbers but didn't have any success but the Pratt and Whitney PT6 is a prime example of durability. The recommened TBO(time before overhaul) on most AIRCRAFT mounted PT6's is 2,000-3,000 hours. The same powerplant is used on the Alaskan pipeline to power electric generators and is rated for a 30,000-100,000 TBO!!!! That equates to anywhere from 4yrs to 11yrs at uninterupted maximum power. Basically put, just as in the GE engine quote, the manufacturers test to extreme limits and then establish a user limit which is much lower. When you read 100% engine RPM on your cockpit gage, that may only be 50-80% of what the engine is actually capable of.

[Craig.]

thank you for the info:)

[Nexus]

Jet engines are far more durable than car engines, for example. Less moving parts = less wear.
And add all the splendid facts above provided by OTTOL, it's easy to understand why engines can endure 14 hrs flights without showing a sign of fatigue.

Speaking about airframes, Boeing had set a design flying life of 30.000hrs for the 707's. But in 1997 one of those old juggernauts had more than 92.000hrs logged, it had been in service for 30 years  :)

[Hagar]

I have little experience of engines but airframes on all commercial aircraft are subject to regular maintenance checks. These vary between simple inspections to complete overhaul. The period between these checks is determined by the licencing authority, the manufacturer of the aircraft & the operator. This is laid down in the maintenance schedule. Some components are lifed & either replaced or overhauled at regular periods. Many components have a shelf life & can only remain in storage for a certain period before being completely overhauled by an approved maintenance organisation. This is without ever being fitted to an aircraft.

In some circumstances this period can be exceeded but only by written exemption from the licencing authority. If you had asked this question 6 years ago I could have given you exact details for specific aircraft types & components.

[SilverFox441]

Various A/C parts have differing life cycle considerations, some are based on hours pressurized (aircraft skins), some on hours of operation (engines), some on landing/takeoff cycles (landing gear), or as Hagar states by calendar time (this can vary from installed time or storage and installed).

When Canada retired our military 707's they had very few flight hours considering their age...but the landing/takeoff cycles were vary high due to all the short haul flights they had done.

[Ivan]

JAL and ANA have the 747-400D (747-400 whitout winglets), after they use up a certain amount of the cycle limit, they are converted to proper 747-400's