Boeing 737 airframe life?

A Southwest Airlines Boeing 737 made an emergency landing after a hole opened up in the fuselage. I was trying to find out when the aircraft was built and/or how many cycles it had been through, and found a story from July 2009 about another 737 that had a hole near the vertical stab. That aircraft was built in 1994.

  1. Has it been said when the aircraft was built and/or how many cycles it had been through; or, does anyone know the N-number?

  2. How many cycles are 737s rated for? Are they retired based on cycles, or hours, or either/both?

I’m not sure which flight you’re seeking information on, so I’ll give both. The one that happened yesterday was Southwest 812, tail number N632SW; it was manufactured in 1996. The one that had a similar problem in 2009 was Southwest 2294, tail number N387SW, manufactured 1994 as you mentioned. Both are 737-300s. One other, especially dramatic, case of decompression that I feel like mentioning was Aloha 243 in 1988, this one a 737-200.

In the United States, 737s may not be flown beyond 60,000 flight cycles without special maintenance procedures specifically related to preventing decompression. So says the FAA. One thing I don’t know is if airlines generally do the special maintenance thingy, or just sell their aircraft to foreign operators before they hit the limit on cycles.

For year of manufacture, I was asking specifically about the one that experienced the incident yesterday. The quoted bit answers most of my overall question. Thanks for mentioning the Aloha flight. I’d meant to, but forgot it in my haste to hit the rack. What prompted the questions is that the 737 is the only modern aircraft that immediately comes to mind when I think of metal fatigue (probably because of the dramatic failure of the Aloha flight). Not that I’m saying that this is what happened yesterday – we’ll have to wait for the NTSB report – but it’s a suspicion.

I wonder how many cycles N632SW had? Southwest is a short-haul operator, and its aircraft can undergo a lot of cycles in 15 years. I don’t know how U.S. operators handle the special maintenance either. I’ve assumed the aircraft were sold to operators in other countries, or else stripped of their usable parts and scrapped. We do have ‘heavy’ pilots who post hear, and they might be able to provide insight.

FWIW I’ve often posted here, when the subject of aircraft age comes up, that the age of an aircraft isn’t a big concern. Old planes and old cars are different. But when I say that, I refer to non-pressurised GA aircraft. Add a pressure fuselage into it, and age becomes a factor because of the number of cycles.

Was this post coherent? I just got up and haven’t had coffee yet.

60,000 cycles. Let’s say an average 737 makes ten flights per day. 6,000 days. Let’s say that a 737 flies 300 days per year. So a 737 should be able to fly for 20 years before reaching its mandated fuselage life, right?

If a 737-600 costs about $60 million, then that means they cost approximately $1,000 per cycle. If the average flight is two hours (NB: Anally-derived number), thus two hours per cycle, then the cost of the aircraft (less financing/interest) works out to $500/flying hour. Did I do that right?

Taking into account the acquisition cost including interest, insurance, scheduled maintenance, unscheduled maintenance, fuel, lubricants, other consumables, crew, parking, and other things I didn’t think of, what is the hourly cost to fly a 737? (I understand that fuel cost is a huge variable.)

I don’t think the 737 qualifies as a ‘heavy’.

Compared to an R22, which I flew, it’s a ‘heavy’. :stuck_out_tongue:

(Empty weight of an R22 is 855 pounds.)

I heard on the news tonight the Southwest 737 had about 40,000 cycles on it.

For what it’s worth, the Boeing KC-135, a military transport/refueling tanker based on the same design that the Boeing 707 (an earlier Boeing airliner) was based on, has been in service since 1956. The newest KC-135s rolled off the assembly line in 1965, IIRC. We still have a few hundred in service, though they require a lot of maintenance and crude language to keep operational (hence the new tanker contract that has been such a huge boondoggle for the last decade or so).

That said, I have no idea if the 135s operate on anything close to the schedule that a 737 in the service of an airline does. I’d be curious to see how many cycles your typical KC-135R had flown between the early 60’s and today. Also worth mentioning, due to the cost and difficulty in getting new airplanes, the military will go through extensive efforts to maintain and refit aircraft, up to and including tearing apart and reassembling entire portions of the aircraft. They just don’t operate on the same business model as the airlines.

When a A/C is sorta hard landed with nothing broke, is there a g meter on some means of recording this event and is this airframe penalized cycles for this?
I know all of us has been there where one is dropped in for what ever reason and where N6325W failed is weak area on most A/C. so has the hard landing or sorta hard landing been brought up?
With short haul A/C this had to happen a few times over the life time before the the A/C is sold or boned out.

Some aircraft have g-meters, and some don’t. I don’t know if commercial aircraft have them. Aircraft were, and I think still are, subjected to destructive testing prior to certification. While excessive-g/pressurisation cycles may not be a combination that is tested, I’m pretty sure they do check for ‘weak areas’. Remember that a commercial aircraft can withstand g’s that would leave a human unconscious.

Here is a photo of N632SW in better days. The damage appears to be just aft of the wing on the port side, based upon its being aft of the over-wing emergency exit. That’s a pretty robust part of the fuselage. It’s not a place where I’d expect a failure to occur after too many excessive g-loads. Do you have a citation that says this is a weak spot in the 737?

WHAT SAY I? I am not an aircraft accident/incident investigator. My gut tells me metal fatigue. But that’s just a non-professional assumption. So I say that we’ll have to wait for the incident report to know what happened.

I believe the most reliable indicator of a hard landing is the blown tires.

Evidence of metal fatigue

That’s somewhat worrisome, since the aircraft had only been through 2/3 of the allowable cycles.

Here is an article about the aircraft.,0,3075044.story

As near as I cam tell, there are previous incidents of cracks in the frame, but not the skin of the aircraft. It also mentions that Southwest has replaced the skin on many 737-300 in recent years, but not this plane. The article also mentions that the plane had gone through a ‘heavy check’ in March 2010.

The flight data recorders onboard commercial airliners do measure the acceleration forces experienced by the aircraft during flight and landings. Some aircraft are equipped with quick access recorders that may also record this parameter. Had an aircraft experienced a hard landing, investigators will have downloaded this data and examined it to determine the forces involved. Following a hard landing, the aircraft is checked for damage in certain areas. In general, if there is pre-existing damage, failure due to cyclic loading (ie pressure fatigue) will occur sooner than normal use fatigue, and will occur at the location of the damage. That’s what the hard landing check should find.

Note that a “hard landing” for an aircraft is significantly heavier/bumpier than what most passengers would think. We’ve all had uncomfortable landings, but statistically speaking, very few people ever experience an actual hard landing that requires reporting/inspection. The forces required are just much greater than those which make it uncomfortable for passengers.

2 other Southwest planes have been found to have cracks similar to the failed one.

American Airlines has had at least one (and I seem to remember two?) metal fatigue/skin rupture incidents in the past few years as well. The one I know for sure was a B757 in October 2009. Both the Southwest and American fleets have aircraft in the 15-20 year range. I know that the CRJ series of aircraft is approaching similar flight cycles/years in service and there is a lot of work being done to try and step up maintenance and study these planes as they age.

Fatigue studies are inherently difficult to do, and there is a lot of research that may not yet have been incorporated into long-term maintenance plans. The new FAA rulesreflecting widespread fatigue damage are part of the ongoing work, as well as general research into aging aircraft. This kind of stuff fascinates me - it’s part of the career I want!

If you think you’ve had a hard landing you tell engineering and they follow the maintenance manual for a hard landing inspection. If they don’t find any problems then the aircraft is returned to service, if they find bent things they fix them.

As mentioned some aircraft have a quick access recorder which will give the engineers detailed information on the incident including g readings. Many airlines today will have an automatic system that transmits QAR data to head office when any limits are broken. In this way the airline will know the aircraft has had a hard landing even if the flight crew don’t report it.