Belly landing: What causes landing gear to fail? [video]

Pilots of LOT Polish airlines Flight 16 weren't able to deploy the landing gear's backup system, spurring some unprecedented questions.

Yesterday, a video camera captured rare and dramatic footage of a commercial airplane making an emergency belly landing.

After discovering something was wrong with the landing system, the Boeing 767 aircraft was forced to touch down at Warsaw's airport without its landing gear. The footage shows the plane skidding down the runway with sparks shooting from the wings as it scrapes the ground. At the end of the day, none of the 210 passengers aboard LOT Polish Airlines Flight 16 were hurt, a credit to the preparedness and crisis management of pilots and the aviation crew who coordinated to have the plane circle for a few minutes to dump fuel as the crew covered the runway with fire-retardant material.

While officials are still investigating what caused the landing gear to malfunction, the explanation from LOT is that the crew had problems deploying the landing gear's hydraulic pressure system. But in that case, what happened to the backup system that's designed to account for these kinds of situations? Patrick Smith, an airline pilot who writes for gives his assessment of what might have happened and why the accident points to a potentially troubling scenario.

The million-dollar question, obviously, is how in the world did all three landing gear units of a modern commercial airliner fail to come down?

I wish I could tell you. I fly 767s for a living and I’m as mystified as anybody else. The plane has both a normal and alternate gear extension system. The normal system uses hydraulics, the alternate relies mostly on gravity, allowing the huge assemblies to more or less free-fall into place if need be. Neither of these, for reasons we’ll learn soon enough, did the trick. Whatever the problem was, it seems to have been something pretty far up the chain of the systems’ architecture, such that neither of two independent systems was sufficient.

The 767 has been in service for nearly 30 years, together with its little brother, the 757. The 767 is the much larger of the two, but otherwise these aircraft are extremely similar, sharing a so-called common type certification that allows pilots like me to be simultaneously qualified on both. In all the millions of landings these planes have made over the past three decades, nothing like this has happened before.

LOT, for its part, is a small but well-respected carrier with an excellent safety record. A freak malfunction? A maintenance mistake of some kind? We’ll find out eventually.

Expert Steven Ganyard told ABC News that he also suspects that both systems may have experienced a mechanical failure of some sort:

ABC News Aviation Consultant Steven Ganyard, a former military pilot, said the Boeing 767 has a backup system to lower the gear, “designed to open the landing gear doors and allow the gear to come down by gravity and lock into place,” if the hydraulics fail.

Ganyard added, “In the 767 there is an electric motor that releases all the door and gear-up locks, allowing the gear to free-fall into a down and locked position.

“There may have been a hydraulic failure,” he said, “but it would appear that the back-up-alternate gear extension mechanism failed as well.”

As of now, much of these theories are wildly speculative. In 2005, Jetblue Flight 292 was forced to make a emergency landing at LAX after its nose gear got stuck and wouldn't deploy. But a system-wide failure, if that is the case, is a different story and will likely lead to a thorough re-examination.

(via ABC News, Salon)


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