Remember back in October when one of Polish airline LOT’s Boeing 767-300ERs skidded to a graceful landing without landing-gear at Warsaw’s Frederick Chopin’s airport? Well, the first report of what happened is out. It’s embarassingly anticlimactic.
Failure of the Primary Landing Gear Extension System
The Boeing 767-300ER has various levels of redundancy. For example, the primary flight controls (ailerons, elevators, rudder) have two backup systems in addition to their primary system.
The landing gear has one backup system (called the “Alternate Landing Gear Extension system”) in addition to the Primary Landing Gear Extension System. So when the “Center” hydraulic system failed as the aircraft took off out of Newark Airport before crossing the Atlantic and heading to Warsaw, the pilots weren’t too concerned. The 767 has three hydraulic systems, Left, Right and “Center”. Some discussion with maintenance people on the ground revealed the extent of the failure was the loss of the primary landing gear extension.
Safe in the knowledge that they had two further hydraulic systems and a backup landing gear extension system, they opted to continue on their journey to Poland.
Upon arriving in Poland, however, they realised that the aircraft was in a much more crippled state than first thought.
Failure of the Alternate Landing Gear Extension System
The pilots approached Warsaw Airport and tried to use the alternate system to drop the landing gear. Normally when the gear is extended and locked in place an instrument in the cockpit shows three green lights, in addition, there is an increase in noise in the cockpit because the nose gear is situated directly under the pilots and causes a lot of audible air resistance. On this particular approach there was neither of these indications that the gear had dropped properly.
The landing was aborted and the tower confirmed that the gear appeared stowed.
The pilots then tried a third means of making the landing gear extend called “gravity drop”. It is just that, they would have unlocked the uplocks on the gear and then performed some mild aerobatics to try and shake the wheels free of their wells.
Obviously, this didn’t work either. The uplocks hadn’t released.
After the plane came to a stop on the runway, the passengers disembarked and the recovery got underway, one of the first things the recovery teams did was to hoist the aicraft up and try to extend the gear. It didn’t work, vindicating the pilots. A check of all systems and circuits then took place. Specifically of interest, noted in the report (here in its native Polish and summarised in English here) were the positions of two circuit breaker switches:
- C829 BAT BUS DISTR – OFF
- C4248 ALT EXT MOTOR – ON
The C829 Circuit Breaker Switch
The C829 breaker is at floor-level on the First Officer’s side of the cockpit. It is located where many crews place flight bags (the bags that pilots carry containing navigational and procedural charts) and not easily visible. Its position is not indicated on any display in the cockpit, and most importantly to the situation that resulted, when the crew aborted the first approach in Warsaw and spoke to their maintenance people, it wasn’t picked up as a possible cause of the problems.
So was this the culprit?
Well, sadly, yes. As soon as the maintenance staff switched C829 to ON, the alternate landing gear system was powered and the gear extended.
Before you judge LOT, or Poland, or the pilots, or the maintenance staff, stop and think. We’ve all punched printers and scanners and thrown them across the room when they wouldn’t work only to find we hadn’t plugged them in… and it’s always easier to analyse after the fact than when you’re in an aircraft doing 300kph over North Eastern Europe with a slowly dropping fuel gauge and no way of getting onto terra firma safely.
My repeated respect to the pilots for landing so perfectly and to Boeing for making the 767 such a tough nut. Even if flicking a breaker switch would have avoided all of this hassle… 🙂