Aircraft Press. Cycles Count

[Tscottme]

I understand what a pressurized aircraft cycle is, even though I only fly spam cans. But how are the cycles actually counted? Is it counted by a piece of equipment inside the aircraft or only tallied by paperwork/records on the ground?

I suspect modern FMS aircraft may have the number available somewhere inside the electronics, but what about older 727 and pre-FMS? How dos one guard against shady operators under-counting cycles/hours? In piston/unpressurized A/C there's a tachometer driven clock and/or Hobbs meter to count hours of engine operation. This number is recorded and can be tracked through the maintenance records. Thanks for a reply.

[Mach E Avelli]

A cycle would normally be one flight ie = number of landings.
If an aircraft is used extensively for local base training, where the aircraft is only doing circuits, an operator may have a different system whereby all landings are logged but only one cycle. This would be highly unusual and hardly worth bothering with, because circuit training forms only a fraction of most flying done in pressurised aircraft.

[vapilot2004]

Quick answer - both paper (hardcopy) and electronic recording (softcopy) of flight hours and cycle data are common in modern air carrier operations.

Longer answer - due to record keeping requirements of the FAA and EASA, and established maintenance procedures, there are multiple sources for flight cycle data, both in hardcopy and electronic form. To name the most common as related to the airframe:

Line Maintenance Log: often updated every cycle.
**Maintenance Log: updated by LM Log and at every inspection/repair procedure.
**Engine Maintenance Logs: updated by LM Log and at every inspection/repair procedure (1 per engine).
ACARS: If installed - automated recording of WOW (weight on wheels) data.
Dispatch Log: updated every time the aircraft is dispatched (added to this is the load sheet signed by the PIC)
*Flight Attendant Cabin Log: updated every flight - (not required)
*Flight Crew Logbooks: Each pilot records time/date/hours/type.
*ATC Logs: Every aircraft movement is recorded.
FOQA via QAR: Voluntary - data added to aircraft maintenance log book

*Typically not cross-checked against maintenance logbooks.
**Periodically signed off and cross-checked by regulator.

In addition to routine maintenance logbook entries, there are flight hour and flight cycle life limited parts that must be inspected at regular intervals. These inspections are integrated into the aircraft maintenance logbook, but are subject to periodic certification by regulators. All maintenance and dispatch log entries are signed off at entry. Electronic cycle and flight hour data is becoming more common with a transfer of the DFDR/QAR data being uploaded after each flight. In addition to the human-generated log data, there are many independent electronic sources of cycle and flight hour data located in various LRU's installed on the aircraft - valid as long as the LRU remains aboard the aircraft in question.

Some areas where historical data can slip through the cracks: Through incompetence or deliberate action, failure to enter or falsification of an entry. Transfer of ownership can lead to missing data, particularly when the transfer crosses international borders. The corruption and lack of accurate maintenance record keeping is not limited to third world operations - there have been many instances of top tier airline maintenance personnel mucking up the record books - via both incompetence and deliberate action. Modern health monitoring computerized systems often share data with the carrier and the manufacturer and limit the possibilities of both incompetence or outright fraud.

Signposts and milestones: AD/AC compliance, SB compliance, maintenance deferrals, manufacturer/regulator required maintenance checks (A,B,C,D), periodic engine inspection, and manufacturer/regulator imposed life-limited part documentation, and unscheduled maintenance operations and incidents are all procedures that serve to document accumulated flight hours and flight cycles on a specific date and time.

[Tscottme]

OK, thanks for the replies.

[skyhighfallguy]

tscottme

I am guessing you are worried about a rapid or explosive decompression?

I know the the DC9 had a static test fuselage in a water tank and was constantly cycled through pressurization cycles IN ADVANCE of any real airliner flying out there.

It was ahead of the oldest real flying DC9 by about 3 times. In other words it had done 60,000 cycles when the real plane was at 20,000 cycles. This is done to note any problems in tests rather than in real life.

While there are some famous blowouts like the ALOHA airlines 737 this is quite rare, quite!

Many years ago a new kind of plane, the COMET had problems and you can read about it in the book : Tale of the Comet. It had the problems before I was born.

And that was a long time ago.

Airlines are best served by excellent safety records. I can think of a Southwest 737 that was relatively new that had a piece of the fuselage open up. But I would like you to understand that the pressurization system has something called an OUTFLOW valve that opens and closes to keep pressure correctly. It is about the size of two passenger windows, so if something blew out like a window it would close and there would be some pressure in the plane. And windows don't blow out very often.


good luck

[vapilot2004]

Skyhigh guy brings up a great aside to this conversation. Cycle lives of aircraft and what can happen when that is exceeded.

The Aloha Airlines 737 loss in 1988 had almost 90,000 cycles on an airframe that had a DSO extension of only 75,000. The loss of one of the cabin crew was particularly tragic, considering the aircraft was landed successfully with a huge chunk of the upper fuselage having gone missing.

The DC-9 has one of the highest DSO (design service objectives) in the business. It was originally rated for 40,000 cycles but in service cycles have exceeded 140,000 landings for some aircraft.

The second rated aircraft for durability in the same category would be the 737NG, which has a DSO of 75,000 cycles, which through a moderate increase in maintenance costs can be extended to over 100,000 cycles.

The next in line for short haul aircraft would be the Airbus A320 series. The DSG (design service goal - same as DSO, different nomenclature) for this aircraft is 48,000 with an extension programme (ESG) allowing for 60,000 flight cycles, again with a (more or less) moderate increase in maintenance costs. There is talk of a stage II ESG that could take an A320 to 75,000 cycles.

I've been told that most commercial aircraft can be kept airworthy for an extended period of time if money is no object. :ok:

Only when major components are showing signs of unrepairable fatigue, such as spars, keel beams, other internal and difficult to replace structural items are the aircraft forced out of service by the regulators. The ancient Grumman flying boats used by Chalks in Miami is an example of this limitation.

[billslugg]

About two years after it happened I met a boat captain in Panama City Beach, Florida who was on a boat near Hawaii and witnessed the Aloha 737 airliner flying slowly and low to the water with the missing fuselage portion.