A 310 / A 320 Problems, one more time.

[Lu Zuckerman]

It seems that my postings regarding potential problems on A 310 and A 320 aircraft have been relegated to the back burner. I have received a lot of technical comment and a lot of approval off line but very few postings on the PPRUNE forum. I’ll give it one more try.

The nature of the design of the 310 and the A 300-600 and by inference other Airbus aircraft can place you and your aircraft in a very difficult situation.

There are two basic problems:

1) The A 310 and A 300-600 flap and slat system are unbonded to the aircraft and as a result can effect the electronic systems on the aircraft. The lack of bonding can also have serious effects if the slats are struck by lightning. Airbus Technical Design Directive TDD 20 A001 states that the two points on the aircraft most likely to be struck by lightning are the nose which has diverter strips and a partially deployed slat. If the slat is struck there is a high probability that the lightning can arc to the nearest slat jack and then into the nearest structure that is bonded to the airframe. That structure is a titanium cup that separates the slat jack from the fuel tank.

Since the flaps are also unbonded a static charge in excess of 1000 volts can build up on the skin surface. When the flaps are retracted this charge will arc to the wing skin or the rear spar causing spark erosion damage and at the same time effect your electronic systems.


2) There is a potential for an internal failure in the power control units that can cause the slats or flaps to move without being commanded while you are at cruise and the CSU is in the off position. If this occurs there is only one way to counter the problem, as the computer can’t stop it. This method is not taught in your training syllabus because it is the contention of Airbus that the Computer will stop the uncommanded action. This was disproved during the design test phase on the flaps and slats however, Airbus was never notified of the problem and neither were Lufthansa and Swiss Air who were flying the A 310.

This is what you have to do:

The Slats are powered by the Blue and Green hydraulic systems while the Flaps are powered by the Green and Yellow systems. If an uncommanded movement is detected in either system both hydraulic systems powering the effected system must be immediately turned off. Select one hydraulic system and turn it on. If the movement continues shut that system off and turn the other system on. If when the first system is turned on, and there is no movement then leave the other system off.

The power available to operate the slats is not sufficient to overcome the airloads at cruise. Below cruise, the slats would most likely be deployed so there is no problem. However if the failure occurs at take off you can have serious problems.
If the flaps are commanded out you have to stop the action immediately because the on coming air loads will assist the flaps to extend. Too much extension at cruise and once again you have serious problems. The same is true for uncommanded retraction of the flaps during takeoff. This happened to an Air Canada A 320 about a year or so ago. The pilots almost lost it. They had to pull every ounce of thrust out of their engines to maintain controlled flight. This was told to me by an Air Canada Safety pilot that was flying right seat on an A 320 while I was up front telling them about the potential problem. The incident was never filed.

I would strongly suggest you demonstrate this on your simulators as Airbus may have caught this problem and corrected it. However I have checked every AD issued over the last ten years and this problem was never mentioned and neither was the lack of bonding covered in an AD.


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The Cat

[N2]

Lu,

There is a lot of flight/dead weight roller contact between the slat track assy's and the wing structure. Would not a static discharge choose this contact route rather than an arc through the slat can?

N2

[Lu Zuckerman]

The system as originally designed utilized plastic bearing inserts on the actuator rod ends which isolated the jacks on both systems. The slat and flap drive lines utilized plastic bushings at all flange points. These bushes were impregnated with a conductive material that was supposed to drain any static charge to either end of the respective drive lines which were grounded to the wing structure and the airframe via a grounded PCU and the wing tip brakes. This was never proved in practice. In fact the conductive bushes would act like an insulator instead of a conductor when pasing high currents resulting from a lightning strike. This could result in the bushes exploding and you would have a complete disconnect of the drive line. The step back gear boxes and the "T" gear box were anodized and therefore did not conduct electricity. Even though both ends of the two systems were bonded to the airframe every thing in between was floating. The above referenced TDD required that Airbus run a conductivity test on the entire airframe. If this test were run they would have found the problem and corrected it. The thinking of the builders of the wing actuation systems was that if they identified the problem they would be financially responsible to correct the problem. Even though the contract required them to noitify Airbus of any problem relating to Reliability, Maintainability and Systems Safety they chose not to do it for the above reasons. They did the same thing when they found the failure that caused a PCU to drive when the computer didn't command it. Another point I brought out in a previous posting was that the Slat / Flap computer was never fully tested and the Flap drive system was never fully tested because the manufacturer of the computer did not furnish the flap drive system manufacturer with a full up computer. They only had 1/4th of a full computer and therefore could not develop complete control functions and resultant trouble shooting on the drive system. The computer manufacturer also refused to comply with the contract which required an FMEA that went down to the smallest piece part. By not developing a FMEA they were never able to tell what effect a failure of a piece part would have on the computer and the ultimate effect on the aircraft. To prove the point,
the first revenue flight for Lufthansa was to Cairo. When they landed they could not retract the flaps. They ended up flying in a non revenue status back to Frankfurt with the flaps partially extended. When they got back to Frankfurt the top mechanics could not diagnose the problem and the computer didn't even know there was a problem. They finally disconnected the system and hand cranked the flaps to the retracted position and they reset the PPUs and the IPPU on the PCU.

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The Cat

[N2]

Lu,

I will put my last post in a different manner. A static buildup/discharge on the slat will take the easiest route to the wing. If it is having trouble going through the slat screwjack/drive system as you say will it not then travel up the slat track arm and through to the wing structure?

One other question; your comment:

"These bushes were impregnated with a conductive material that was supposed to drain any static charge to either end of the respective drive lines which were grounded to the wing structure and the airframe via a grounded PCU and the wing tip brakes."

Would not a direct ground also be provided to the drive system through the shaft torque limiters?

N2

[Gnd_Chk_Satis]

What a load of toss!! written, I would humbly suggest, by someone with an axe (or two) to grind.

Of course slats / flaps on the Airbus aircraft are bonded to the rest of the aircraft!?!....having seen a number of bonding checks carried out....bonding is fine...and as for SFCCs not being tested etc etc....well leave that one to the chemtrails forum...

Having said that--we all know of several instances where Airbus design and practice has not been all is should have been..but then the oppostition are far from perfect either. For my money the Airbus product is good..very good..and slanging them off with such BS is just a cheap shot best left for the train spotter brigade.

Gnd_Chk_Satis...Please Report Further.

[Lu Zuckerman]

The first reply is for N2:

Regarding the slats,what you say may be true.
However the conductivity of the Rose Bushes was never fully proven. Now, there is an Airbus service bulletin out that tells the mechanic to make a check of these bushes and if they are worn or, if they show any electrical conductivity they should be replaced. If the Rose bushes were in fact electrically conductive now they are being replaced by bushes that are totally non conductive. That is what started me on my latest crusade. I contacted Transport Canada and the FAA requesting a copy of their respective ADs that were written against the original service bulletin written by Airbus. When I got them they were completely different. Both had been translated from the French Language and both addressed the problem in a completely different way. I contacted them both telling them of the problem. Transport Canasda contacted the DGCA who in turn contacted me. They asked me to explain the problem regarding bonding and the possibility of uncommanded operation of the flaps and slats. I complied with their request sending them several pages via email. I asked them for their comments. I waited for several weeks and sent them another email. They never responded.

The problem is not static charge drain through the system it is in the inability of the system as designed to conduct the high currents resulting from a lightning strike.

If Lightning hits the sharp edge of the partially extended slat it will take the path of least resistance and arc to the first slat jack and at that time the jack screw is inside of the cup that separates the fuel from the outside world.

Regarding the conductivity of the torque limiters you may be correct but first the static charge has to get there. Even if the charge could pass through the system via the Rose Bushes we still have two things to contend with. 1) The inability of the Rose Bushes to conduct the high currents resulting from a lightning strike and 2)Any rose bush that exhibits conductivity is going to be replaced by a Vespel Bush that is non conductive.

The initial test to verify the system conductivity was performed on the Iron Bird for the Slat system. It was most likely performed using a standard multi meter. A similar test was performed on the Flap iron bird and again, most likely using a similar device. The iron bird installation is exactly like the aircraft installation and in running the continuity check there was no conductivity through the system and no conductivity from the system to the iron bird. When this check is performed on the aircraft after final assembly the instrument used is most likely a megohmmeter which can generate higher currents.

The test performed in accordance with Airbus TDD 20 A001 requires that the resistance between 22 different points on the airframe in respect to specified other points on the airframe are as follows: An electrical resistance measurment shall be carried out between each point in column A and the corresponding point(s) quoted in column B

The measured resistances shall not exceed 10 milliohms if the measurment points are made of aluminum or copper alloy, and 100 milliohms if one at least is made of stainless steel or titanium. That statement is on page 30. On page 33 there is a concession. 50 milliohms may be accepted for slats and flaps fitted on tracks.

My question is, did Airbus perform these checks? The document in question was not approved for use at the time the first group of aircraft were already in revenue status.


Now we get to the response to Gnd_Chk_Satis:

Yes I have an axe to grind and it is not with Airbus. It is with the certification authorities. My only question with Airbus is whether they performed the test. Regarding Airbus design practice is concerned I have no qualms. The subject document is perfect in every way and could have been lifted from a text book on aircraft grounding practices. The problem is that the major partners in the flap and slat drive system and the integration contractor and the wing designer would not support any design changes because they did not want to be financially responsible for the change. Every thing I said about the FS Computer not being fully tested and the FMEA not being constructed per Airbus requirements is fact.

You missed the major point of my posting and that is the flaps and slats can operate without being commanded and the computer can't stop it. That is why I provided the counter measure and that is why I stated that it should be checked in the simulator because by now Airbus should have caught it but, there are no ADs to make the necessary changes. In 1983 or 84 I notified the FAA about the problem and it took six months for them to take action. When they did, the Vice President and the program manager of the German company responsible for the flap/slat drive system design were fired. But, the design was never changed. So, if you are flying in an Airbus aircraft i would suggest that you keep my instructions in mind. One final point, I know these facts to be true but I ask the question, how many other companies involved in system or appliance design kept their little secrets to them selves in order to maximize their profits. Remember this point, contracts are usually let to the lowest bidder. That is a question pondered by the astronauts when they got into the Apollo Capsule.

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The Cat

[Lu Zuckerman]

One other point. If the slats and flaps are in effect ungrounded (unearthed for the English speakers) there could be another situation and that is the development of streamers. These are electrical charges that can arc from and ungrounded system or even a small component and the charge can be sufficiently strong to blow a hole in the aircraft in trying to connect with an attached lightning strike. This happens a lot on composite structure that is not bonded to the structure. It also happens a lot on Radomes on the nose of the aircraft.

Airbus aircraft have diverter strips on the Radome so this is not a problem. At least on the nose. And, the flaps and slats are composite.

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The Cat

[atomic]

Lu!! You're not being ignored! But what are we going to do now?! I think this forum is good to raise awareness and I will definitely bring it up in my company, but what kind of response do you expect here??!!

[Lu Zuckerman]

The fact that you are going to bring it to the attention of your company is response enough. The first post I made on this forum about potential problems on Airbus aircraft got very few response on line but my email was overflowing. Most of the replies were from members of IASA (International Aviation Safety Association). They suggested that I provide all of my information to division of Phillips Publishing in Maryland. This group publishes a safety news letter dedicated to airline related safety problems. They indicated in a telephone conversation that they would look into my claims. That too is a good response.

Safe Flying

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The Cat

[TheShadow]

Some relevant ASW and IASA URL's
http://www.aviationtoday.com/spjaward.htm
http://www.aviationtoday.com/reports/
http://www.aviationtoday.com/reports/index.html#Interviews
http://www.iasa.com.au

http://www.geocities.com/Heartland/Oaks/8553/bwbgrd8A.gif

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Who knows what evil lurks in the hearts of men?