Monday, October 17, 2005


Steve's Video Of The Day: "Torching"? Let Me Tell You A Thing Or Two About "Torching"............!

"Torching" is a phenomenon that occurs when raw fuel passes through the combustion chamber of an engine unburned, and then is ignited in the exhaust phase. It happens quite often on radial engines during cold starts, and is quite a spectacle, especially if one is starting up while darkness is still enveloping the early AM. While not overly dangerous, normal torching can be quite disconcerting to the uninformed passer-by who just stopped to watch the airplanes. Jet engines will also torch if proper procedures are not followed, and a "hot-start" may be experienced, though not always. Anyways, read the following from the webmaster at, and then watch the video in question, and turn up the speakers. It is a visual experience!
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737-500 Engine Start

April 19th

I've been away for the last two weeks, so I was unaware of the popularity this video had suddenly gotten (it's apparently been posted on bulletin boards all over the web). It's starting to wear off now, I suppose, but I assume some of you are still interested in what's actually taking place on the video. There's a lot of assuming, and although some is right, a lot is also wrong.

First of all, there are no Pax on board the aircraft. We were three people in the cockpit (me, and an additional two) and two people outside (one of which filmed the clip). All of us are maintenance crew.

What is shown on the clip is what is known as a "wet run". The engine had just been installed (replacing an engine that was due for maintenance), and this is the first startup of the engine after a long storage period. Flames like this on wet runs are actually quite usual (or so I've heard), just not this big.

What happens during a wet run is that the engine burns out any residual oil inside the engine that was left there during the storage period. It also burns a certain amount of fuel because the engines usually ignite slower at first startups after storage. The thing that happened to us was that we didn't get any ignition on the first try, thus we filled the engine up with quite an amount of fuel. Before a second try, you're supposed to dryblow the engine with the starter to get the fuel out. That's where we got lazy and didn't do our job properly. On our second attempt, we poured fuel into the engine once again and when it finally ignited we got a result worthy of remembrance.

Some of you might find it unbelievable, but there was no damage to neither engine nor flaps after the incident. Normal on-installation test procedures were taken on the engine, and the plane left the airport with Pax on board the next day.

If anyone has any additional questions, you can reach me at

PS: The fact that it was filmed was pure coincidence. We had no intentions on making any flame at all.
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VIDEO - "Torching"? Let Me Tell You A Thing Or Two About "Torching"............!

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