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aviatorpk
29th Aug 2002, 10:31
Are the wing spars of high time Airbus B4 cracking ?????:confused:

Willit Run
30th Aug 2002, 05:48
I sure as heck hope not, I'm still flying these old traps!
But, I've flown a lot older, so,

why do you ask? do you know something the rest of should?

Brenoch
30th Aug 2002, 06:26
Check signature.. :)

aviatorpk
30th Aug 2002, 08:33
PIA had to ground their Airbus B4 for few days to carry out the inspection of wing spars

Volume
30th Aug 2002, 09:13
Any wing spars on ageing aircraft have cracks. Most of them are very small and only detectably by special inspection technologies (i.e. eddie current inspection), some of them are lage and visible during routine inspection.
There are crack findings in service for any type of plane of any age, this normally leads to SBīs (Servive Bulletin) by the manufacturer where all operators are told to do some sort of inspection, replace some fasteners by oversized type, do coldworking of rivet holes, install some sort of doublers or reeinforcement brackets or something like this. The authorities are notified, and if they think this is a larger problem, the SB is made mandatory by releasing an AD (Airworthiness Directive). There are hundreds of ADīs every year regarding cracks for different types of aircraft. This is all totally normal and just a consequence of the fact, that large transports are not designed to last forever, but to make profit with the least ammount of maintenance. So they are designed to take some cracks, even in the wing spars, without consequence.

For the Airbus B4 models there had been lots of crack findings and structural rework or reinforcement in the past (but even less than on other aircraft types by other manufacturers) but the only recent problem I know at the moment, regards gear rib 5 (the wing rib where the main gear is attached to). This seems to be nothing to worry about, this rib can be inspected visualy without problems and can be replaced in complete if neccesary, or just repaired locally if the cracks are small enough. If no cracks are present, reworking some fastener holes and installing oversized fasteners will increase service life of the parts and avoid further cracking.

Enjoy flying the B4 as long as they are existing, no need to worry

eng1170
3rd Sep 2002, 00:03
Volume, i may have mis-understood the context of your post but to say that "any wing spars on ageing a/c have cracks" seems to be a very bold statement. I work on a/c that are classed as ageing a/c and thus subject to CPCP inspections and checks and yet I would like to think that if a spar crack was found on any of our a/c then it would be grounded until repair action carried out and also a fleet-wide check carried out. I may have mis-interpreted your post but I couldn't help feeling that this sort of thing is a normal occurrence. My understanding of the principle of "failsafe" structure is that, yes a crack could develop and be missed on an initial inspection and that if the crack spread to the point that the section in question failed, then the remaining structure is designed to bear the loads under all flt/gnd conditions until the next inspection where the defect would be so obvious it should be picked up. I would be interested to know how often you come across cracks that are "large and visible during routine inspection" and in what area's of the structure. I have only experience on one type and certainly don't come across defects as severe as this example very often at all.

I apologise in advance if I have mis-understood and did not intend any offence, but your comments surprised me somewhat, i look forward to a reply

Eng

Volume
3rd Sep 2002, 07:47
As I stated before, there are always some cracks, but they are normally really small, just in the order of microns and only detectable by special inspection methods. They do not reduce strength of the spar, because metal has the ability to ībridgeī such cracks by deforming plastically at the crack tip. Nevertheless such cracks grow with flight numbers, most of them so slow that they never become critical.

One interesting example of aircraft fatigue cracking is the Lusaka Accident (http://www.geocities.com/CapeCanaveral/9575/770514-0.htm) where a 707 lost its stabilizer due to fatigue cracking of a spar cap.

īThe total number of flights between the initiation of the fatigue crack and the final failure of the upper chord is estimated as being in the order of 7,200 flights with some 3,500 flights of propagation occurring across the exposed top surface of the rear chordī

This means the crack was existing a few 1000 flight cycles before it became visible (but was not detected), and afterward grew further for thousands of flights before total failure of the spar occured.

You donīt worry about the thousands of holes every wing spar has (rivet holes), so donīt worry about the hundreds of cracks that are much smaller than the holes ;)