I was recently involved in a flight that had issues before take off. The plane was an Airbus 321.

It was explained to me as being a "wing loop fault". The problem was that the ECAM messages were displayed differently each time and were inconsistent. The flight was aborted just before take off (for safety reasons) but the problem was fixed soon after by replacing a part.

Can anyone explain this problem with the wing loop to me in more detail. What could have gone wrong and what was the likely fix.

Also, what maintenance and pre-flight checks should occur on the "wing loop"?

Sorry for any vagueness in my question, I didn't receive much information.


  • This was on aircraft G-OMYJ around the 24th August 2013
  • My route was (EMA) --> (DLM), flight TCX5894. But the fault may have occurred on the previous flight. The details are unfortunately hazy. Is there anyway of me finding the whereabouts of the plane in the days leading up to this incident?

My guess is that there was some circuitry that was playing up. While I'm not sure about 'Wing Loops' specifically, for what I think is a similar example the Airbus A320 series has fire loops in the engines.

There are two fire loops. If I'm right, it's got little thermal sensors along way, which disrupt the current if they get too hot (or if the wire is broken). Logic gates ensure that both loops must be 'high' for the fire warning to go off. If one is not working, it works from a single input.

Assuming both of these were working from the beginning, I think it throws a FIRE DET FAULT warning on the pilot information display if one triggers without setting off the other one. I'd imagine that maintenance either disabled the faulty loop within those allowed by the Minimum Equipment List or by changing the part. If it was quick, it was probably the first, but they're not going to go telling passengers that they disabled safety equipment :)

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  • $\begingroup$ Hi.. Can you provide the details of the "Minimum Equipment List" and which loops would be allowed to be disabled. Also, for the record, the resolution was that an unspecified part was replaced. $\endgroup$ – Sam May 5 '14 at 12:08
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    $\begingroup$ @Sam it's not quite easy to read off, but here's a copy: fsims.faa.gov/PICDetail.aspx?docId=M%20A-320%20R22a $\endgroup$ – Thunderstrike May 5 '14 at 12:40

It might be a problem with the loops of sensors for the fire detection systems etc

For example: ECAM message "FIRE LOOP A FAULT" (ATA 49: APU)

Both engines and the APU each have two identical loops, A & B and a computer- FDU (Fire Detection Unit). A fire warning is given when both loops reach the proper overheat condition. If one loop fails the other loop is able to generate the warning by itself. A fire warning is given if both loops fail within 5 seconds of each other.


The leak detection system uses a single loop for the pylons and APU to detect hot air temps associated with duct leaks. Dual loops are used for the wings. If both of the dual loops detect a leak a warning is given, unless there is a fault on one, then only one loop is required to give a warning.

From Eric Parks training notes.

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