It Was Supposed To Extend
When a design is supposed to be bulletproof and a procedure is supposed to work every time, and it doesn’t, you start off thinking the crew didn’t execute the emergency procedure properly. However, first impressions are not always right. Good investigators proceed carefully, step by step, to get to the truth. A regional airline gear-up landing I helped to investigate in 2013 is an example.
When the crew attempted to lower the landing gear of a DHC8 turboprop on an approach to runway 4R at Newark Airport (EWR), the left main landing gear (MLG) showed a red unsafe indication. The captain received approval from the EWR tower to perform a fly-by and the tower confirmed the left MLG did not appear to be extended. The crew proceeded to run the appropriate checklists to extend the gear using the alternate gear extension system, but after more than an hour and a half, the left MLG remained up. Running short of fuel, the crew retracted all the landing gear and executed a safe, but noisy, landing on the belly of the aircraft. The passengers and crew evacuated in an orderly way and no one was injured.
The DHC8 landing gear is normally operated by hydraulic pressure. When the hydraulic system fails, the alternate system, operated manually by cables and assisted, if necessary, by a hand pump, should work. The alternate system requires the use of manual force on cables, and pilots don’t have to do alternate extensions very often, so it was very possible the crew had not operated the cables or hand pump properly.
After interviewing the crew, I began working my way through the company’s pilot operating handbook, studying the landing gear system and the emergency procedures that pertain to it. Some of what the crew told me didn’t quite jibe with what I was reading in the handbook. For example, the crew told me there was no guidance in their handbook or checklist to help the captain decide whether to land with all gear retracted or with partial gear extended. I thought that was odd since the airplane had been in service a long time and its combination of a high wing and large props could be quite hazardous if one MLG didn’t extend. Surely this type of emergency had happened before and sound gear-up guidance developed.
Also, the crew had flown down final approach with the landing gear warning horn blaring, and that seemed wrong. There should never be a situation where a crew has to fly an airplane with an aural warning sounding continuously like that. However, the handbook did not address how to handle the situation. I wondered what I was missing.
I decided to call the aircraft manufacturer and get a copy of its procedures. I noted that over the years the manufacturer had made a number of changes to the alternate landing procedures that were called “safety of flight supplements,” and there was some interesting information in two of them.
The first one, issued in 1997, emphasized the importance of applying sufficient force on the gear release handle. A DHC8 had landed gear up because the crew had not used enough pull force on the main gear release handle. The supplement suggested that proper procedures should be taught in flight or simulator training.
The second supplement, issued in 2009, provided detailed guidance on landing with the nose gear retracted or unsafe, landing with one MLG retracted or unsafe, and landing with all landing gear retracted. For the most part, information in these supplements had not been incorporated in the airline’s handbook. There was a note at the bottom of the company’s alternate gear extension checklist about high gear release forces, but it looked to me like an afterthought. If you want the crew to be aware of high forces, you should put that statement in the body of the checklist where they’ll be sure to read it when they’re moving the cable handle.
Some of the facts that were emerging supported the idea that the crew just mishandled the emergency, and could have gotten the gear down with enough effort and diligence. The manufacturer’s safety supplement strongly suggested crews should be able to get the gear down using the alternate system if they applied enough force to it.
I noted the crew was at the end of a very long duty day. The event happened just before midnight and they had been on duty since just after noon. It is well established that human performance declines after being awake 12 hours and during periods of circadian low, and that was true of this crew. They could have missed a step or misjudged the force needed to get the errant MLG down.
On the other hand, there were other facts that didn’t seem consistent with simple crew error. Both pilots were experienced on the airplane; the captain had 22,000 hrs. and the first officer had 1,700 hrs. on the DHC8. Both pilots had previously performed alternate gear extensions successfully. The FO had performed an alternate gear extension twice before and was familiar with the amount of force needed on the handle. The hydraulic system that operated the landing gear had not failed, so even 3000 PSI hadn’t been able to move that gear off its uplock. I was also struck by how much time and effort the crew put into trying to get that gear down. They went through all relevant checklists multiple times, retracted and extended the gear multiple times, and did two flybys. Both pilots took a turn at trying to pump the gear off the uplock using an auxiliary hand pump, and the captain did his best to confer with company officials on the radio to come up with a solution. They even tried to apply a positive G load on the airplane while extending the gear, but it was to no avail.
When aircraft systems investigators inspected the landing gear, they found the left MLG uplock roller had seized, meaning it would not turn, and a groove that was at or beyond wear limits was worn in the left uplock. Using a strain/force gage, they measured the force needed to move the left MLG off its uplock to be 240 lbs. One investigator could not move the manual gear extension handle even when hanging his full weight on it.
Clearly the initial idea that the crew erred was wrong. A gear extension system that was supposed to work every time didn’t. By gathering all the facts, being systematic, and withholding judgment we got to the actual cause of the accident. To its credit, the company took immediate steps to remedy their procedures, communications and maintenance practices. But they rushed to judgment about the crew’s performance. After the accident the captain received some company “retraining,” as though he had done something wrong.
But for the captain’s experience and skill, the accident could have been much worse. He made the right decision to land with all gear retracted and he put the airplane right on the runway centerline. He kept the wings level, which prevented the props from striking the ground and shattering, and he commanded a safe and prompt evacuation. He did this even though the manufacturer’s guidance had never been incorporated in the company handbook or checklist and even though the company radio advisor didn’t know about the guidance either. It was a pleasure to me as an investigator to see a crew handle a tough situation so well, even though it took a while for me to confirm it.