Ask Captain Lim ~ All about Aviation

Dear Capt Lim

Following the lucky escape of the Air Transat A330-200 from fuel starvation in 2001 (as shown in the documentary "Air-crash investigations") I started thinking about how pilots are alerted to a fuel leak. Manual computations of the FOB (fuel on board) are essential, but a computerized warning should also occur. Based on my knowledge of onboard computers of both the A-320 (which I assume is similar to the A-330) and the 747-400, from the PMDG and the PSS flight-simulator models, I understand that there is no EICAS warning that directly alerts the pilots to a possible fuel leak. Is this indeed the case? If not, what message appears and what sequence of events triggers it?

I realize that you fly 777*s but I guess you have some general knowledge about other aircraft as well.

I would like to suggest implementing an automatic fuel leak detection scheme that is based on a comparison between the actual current FOB and the value that the computer calculates based on the initial FOB minus the fuel used up to that point. It should be straightforward to add such a calculation to the FMC and have an EICAS warning message "suspected fuel leak" appear if the actual FOB is, say, a few percent smaller than the calculated value. The EICAS message should also inform the pilots by how many percent the actual FOB is too low, allowing the pilots to see if the discrepancy increases with time and at which rate. The message would be a clear indication of a "possible fuel leak", and it should avoid erroneous opening of the cross-feed valve, as the Air- Transat crew did.

I guess that the engineers designing the planes thought of this option. But I can*t figure out why it is not implemented? Any ideas?

I found an FAA amendment 39-14453 dating Feb. 3, 2006 advising crews of A330*s and A340*s on the importance of limiting the severity of a fuel leak as occurred in 2001. However, these guidelines do not improve the speed and ease at which the pilots can positively identify a fuel leak.

I am eagerly waiting to hear your comments,

Sincerely yours,

Dr. Ron Arad (a physicist)

Hi Dr Ron,

I can see your logic in proposing an automatic fuel leak detection system to make it easier for the pilots in the cockpit to detect this problem. Even on the Boeing 777, there is no clear-cut checklist for fuel leak. The closest that we have is a ?Fuel Imbalance? check that would eventually lead to the fuel leak problem.

Regarding the Air Transat A330-200 problem in 2001, there were indications that the crew had made an error in recognizing a genuine ?Fuel Imbalance? EICAS message.

Anyway, if one follows the fuel imbalance procedures, and if there is a leak somewhere, it would be detected through the troubleshooting process.

Obviously, to detect a fuel leak, the most efficient method is to compare it with a tank without a leak or measures the rate of fuel loss - i.e. whether one main fuel tank quantity is decreasing faster than the other and in the case of the Boeing 777, any increase in fuel imbalance of approximately 500 kilograms or more in 30 minutes would be considered a fuel leak.

However, there are times when the metering unit gives false or erroneous readings. Hence, I believe, the design-engineers* philosophy was that it would be better to have a procedural "Fuel Imbalance" checklist to preclude other problems first before pin pointing to a real fuel leak.

Whether this is a good or bad idea is very subjective. Yes, I do agree with you that the technology is there for an automatic fuel leak detection system. It should come with a warning such as ?Suspected Fuel Leak - Right Engine? rather then the indirect message "Fuel Imbalance". I am still not exactly clear as to why this isn*t implemented.