The smell of smoke before take-off

[forcedtofly]

Hi Captain Hutch, and everybody else, too, :):

I posted about this a while back, but no one ever gave me an explanation. I'm wondering if you can.

The last time we flew, as we were sitting on the runway before take-off (and in the back of the plane), my husband and I began to smell something burning. It was a very strong odor, and since I'm so scared of flying, I called the flight attendant over and asked her what it was. She didn't go into much detail and just said something about "fuel burnoff" or something like that. I felt a little better that she wasn't concerned, but I'd still like to know what exactly that was. Can you explain this to me? I am flying again in March, and I'm trying to get myself prepared mentally. The burning smell really bothered me, and I want to know when this should worry me and when it's just normal. Thanks!

[Captain Hutch]

Dear Forced-to-fly,

That is a very good question and I am glad that you asked the flight attendant about it. I always recommend to my flight attendants that they let me know immediately about any concerns of the passengers about matters like this. I don't mind delaying the takeoff to clear up any potential problems especially related to smoke and peculiar odors. My first question to the flight attendant is to try to identify the type of odor. Possible odors and their cause: electrical smell--burning wires; oil burning--slight oil overflow after Auxiliary Power Unit (APU) shut down; "burnt stove"--F/A may have left something in the oven in the galley and not turned the oven off, or coffee-maker hotplate may have something on it; component in the airconditioning unit may have overheated; outside odor from other aircraft landing or taxiing may have worked it's way thru the system into the aircraft; defective lighting fixture in the lavatory.

In your specific case, it may have been the smell that is associated with APU shutdown and an experienced flight attendant will probably be very used to it and thus her reaction. You did not specify whether the odor continued or not--if you continued to notice the odor after takeoff I would mention it to the flight attendant again.

Thanks once again for bringing up an important point.

Hutch :tiphat:

[forcedtofly]

Thank you so much for the reply! I never really thought of all those possible sources of a burning odor.

We noticed that the smell started going away once we took off. It got very strong as we started to taxi and then as we were sitting on the runway for a little while, but then gradually it went away. It really made me freak, but like I said, the flight attendant did a good job calming our fears and even told us that we had done well by asking about it. A lot of people around us turned out to see what her answer was, so I knew that they must have been wondering, too, but were too afraid to ask! :)

Thanks again for the explanation. It will help me a lot if this ever happens again.

[Captain Hutch]

Dear Forced-to-fly,

The fact that the odor went away shortly after takeoff inclines me to believe the smell was associated with the APU. As I have covered in other threads, the APU is a small jet engine that is mounted within the fuselage, usually in the tail in most aircraft. The APU has the capability to run the electrical systems and air conditioning and pressurization when the aircraft is on the ground, taxiing or at the gate, or in the air up to certain altitudes. Often times the power and air conditioning systems are run by ground units while the aircraft is parked at the gate. The APU also has the capability to provide airflow that will turn the compressor blades on the jet engines to enough RPM that the engine can be started. Once we get the engines started and taxi away from the gate, we usually switch over to ship's power and then somewhere during the taxi to the runway we will shut the APU down. If it looks our takeoff may be delayed by Air Traffic Control, we might shut the engines down but still leave the APU running. Sitting in the rear of the aircraft puts you relatively close to where the APU is mounted, so I suspect that some of the APU odors of fuel and oil associated with jet engines may have worked their way into the cabin. Depending on which way the wind was blowing relative to how the aircraft was taxiing or parked, the wind may have contributed to the odor being pushed into the rear of the aircraft. I am not familiar with any barriers or seals which might be in place to keep the odors away from the cabin, although maybe one of these components might have been defective.

Thanks again for bringing up an important item.

Hutch