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Landing Gear Failure (OGHFA SE)
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|Content source:||Flight Safety Foundation|
|Human Factors Aspects||Professionalism, Workload, Stress, Judgment, Decision Making|
|Operator's Guide to Human Factors in Aviation|
|Landing Gear Failure|
The Incident as a Situational example
You are at the end of a transatlantic flight and start your approach. In addition to your first officer, your crew is complemented by a non-handling cruise relief pilot (CRP) for duty time extension.
After takeoff, the landing gear took a little longer than usual to retract, but there were no abnormal indications or alert messages, and hydraulic system quantity indications were normal.
The flight proceeded uneventfully except that during cruise, as part of routine checks of systems, the no. 6 brake temperature indicator appeared to be malfunctioning.
The flight continued normally until the airplane was about 8 nm (15 km) out on final approach to the runway. On selection of landing gear down, an unsafe alert appears, telling you that the left main gear is neither down nor locked and that the gear door is only partially open.
What is your strategy?
As this condition persists in spite of recycling attempts, the first officer, who is the pilot flying, initiates a go-around. It is initially thought that recycling the gear would successfully deal with a mere indication problem, a computer software issue or a micro-switch malfunction, but all ensuing attempts fail.
As the airplane is going around, a “Green Hydraulic Low Level” alert appears, and you suspect a system leak is probably the cause. However, on recycling the gear again, this indication disappears.
Once established in the holding pattern, you start the “Landing Gear Gravity Extension” procedure in the quick reference handbook (QRH). The operations department is informed and receives printouts from the airplane. After consulting the company fleet manager, it is believed that there was a gear-out-of-phase sequence. You are going to attempt rectifying the gear problem by selecting nosewheel steering on and off. This attempt is not successful.
The first officer makes a low pass over the airport, which leads a company engineer in the tower to conclude that the gear is “hanging in the bay” and only partially deployed. Air traffic control (ATC) relays a company request for a second flyby. You then take over flying for the remainder of the flight.
Due to airport traffic, the flyby would mean conducting another complete instrument landing system (Instrument Landing System (ILS)) approach. In addition, low fuel alerts have begun. Thus, you do not consider it prudent to conduct another flyby.
What are your options?
Several options are pursued to resolve the problem:
- A high-load-factor maneuver. Jolting the airplane hard on its side to free or loosen the gear has no apparent effect.
- A touch-and-go on the right main landing gear to cause the left main gear to be shaken free. However, because of the relatively low fuel condition and since you have never practiced this in a simulator, you do not do it.
The cabin crew is fully informed of what is going on, and the passengers are briefed about the overflight. After all efforts to lower the left main gear have been exhausted, the cabin crew is told to expect an emergency landing, to order the brace position upon touchdown and to evacuate the cabin after the aircraft stops on the runway.
What do you do now?
You decide to position the airplane for landing and formally declare an emergency. The weather is excellent, but daylight is beginning to fade.
The two first officers handle the “Low Fuel Warning” procedure to clear the cockpit of all orange or red warnings and to ensure all drills have been performed. As pilot flying, you are satisfied with the situation.
Because the airport has two parallel runways with terminal buildings in between, ATC proposes the left runway so that possible contact of the left engine with the runway would tend to cause the airplane to veer away from the central area and terminal buildings.
For this reason, too, the fleet manager suggests touching down on the right side of the left runway.
The CRP, reading from the expanded notes in the airplane operations manual, reminds you that the center landing gear is still extended, while for structural reasons, its use is precluded.
What is your reaction?
You request a circuit on base leg to provide additional time to perform the QRH “Landing with Abnormal Landing Gear” procedure. The gear is retracted, and the procedure re-initiated from the beginning to ensure that all actions are completed in the correct order and that the airplane is in the correct configuration.
The procedure calls for the crew to shut down all engines just prior to touchdown. However, during a previous review, you elected to modify the procedure and brief the crew to shut down the no. 1 and no. 4 engines on initial touchdown, then to shut down the no. 2 engine at your command and the no. 3 engine as the airplane settles onto its left side.
You fly the final approach manually. All engines are shut down as briefed. As you attempt to hold the left wing up as long as possible, the no. 4 engine strikes the runway, generating friction sparking and very brief fires.
As soon as the airplane comes to rest on its left wing, crew liaison with fire service personnel confirms there is no fire. You immediately order an emergency evacuation, which takes place with only very minor injuries to passengers and crewmembers.
Examinations reveal that the gear had been jammed by a wheel brake torque rod that had disconnected from its brake pack assembly and had become trapped in the keel beam structure. The associated torque rod pin was later found at the departure airport.
Data, Discussion and Human Factors
Pilot-Controller and Pilot-Airline Operations Coordination
During the troubleshooting phase, the airplane remained within VHF radio range of its company operations, where full support could be provided to the pilots in their attempt to overcome the gear deployment problem and manage the situation, including:
- Various attempts to solve the landing gear problem technically by talking with airline engineering and operations personnel.
- The possibility of diverting to another airport, with ground services being informed accordingly to prepare to accept the airplane.
- The decision to carry out a low-level overflight.
- The airline’s observations from the control tower.
- The attempt to fly high-load-factor maneuvers to shake the gear loose.
- The advice to touch down on the right side of the runway to avoid a runway excursion.
ATC provided excellent support to the crew and the airline. During the troubleshooting phase, ATC established communication with the crew on a discrete frequency, so that other airplane transmissions would not interfere with or block transmissions. ATC also judiciously proposed that the crew land the airplane on the left runway to avoid veering toward the terminal buildings after touchdown.
Finally, the rescue and fire fighting services were well prepared to deal with the airplane. They were able to promptly inform the crew that there were no fires and to coordinate the evacuation.
The pilots demonstrated excellent coordination and did not show any sign of fatigue or stress despite their overnight duty. The captain initially immersed himself in overall monitoring and decision making concerning the flight scenario, as it was initially decided to leave manual control, ATC and drills to the first officer as PF. This was subsequently reversed when the problems had been clarified following the tower overflight — the first officer reviewing basic drills, and the captain taking over flight handling for landing.
The three pilots worked well together as a team and successfully implemented the planned division of duties per crew resource management (CRM) principles. Each pilot was able to make a valuable contribution to the team and displayed a high degree of initiative and motivation.
The direct VHF radio link to the airline was undoubtedly beneficial to the crew to create a non-stressed and extensive decision-making chain.
The third pilot alleviated the workload of the other pilots and made himself useful by taking on the responsibility for coordinating with the cabin crew and seeking out the appropriate reference material from the airplane operations manual.
Just prior to landing, he also noticed on the expanded checklist that the center gear was not in the correct landing configuration for the circumstances. Had this not been noted and had the airplane landed with the center gear extended, more extensive damage would have ensued.
The cabin crew was kept fully informed of the situation, and the passengers were briefed about the tower overflight. After trying all the options to lower the left main landing gear, the cabin crew was briefed to expect an emergency landing and a planned evacuation after coming to a halt on the runway.
Trained to operate the airplane with a two-pilot flight crew, the captain said that if there had not been a CRP aboard, he would have used a cabin crewmember to coordinate with the other staff.
Professionalism and Teamwork
Throughout the flight, the flight crew showed excellent airmanship with all decisions being a combination of good discipline, skills, knowledge, situational awareness and judgment. The news media focused on the captain as the individual who saved the day, but he insisted that the outcome resulted from teamwork between cockpit and cabin crewmembers.
In response to the unsafe landing gear deployment alert on the first approach, the crew correctly decided to conduct a go-around and take time for a thorough assessment of the situation. Situational awareness and judgment were enriched through gathering and assembling as many facts as possible.
When the airplane’s fuel system generated a low-fuel-quantity alert, the captain judged that a second overflight was not appropriate and decided to plan for a landing.
The captain's decision to modify the QRH procedure with respect to the engine shutdown sequence was quite prudent, since he wished to retain the airplane’s electrical and hydraulic systems for as long as possible in order to prevent any negative consequences to flight control. This procedure was subsequently adopted as the manufacturer's recommended technique and included in a revised QRH.
After the overflight had taken place and the fuel system low-level alerts had been generated, the workload increased markedly. There was an almost continuous stream of communication between the pilots, ATC and the airline. Once committed to the final approach and landing, the captain requested a precautionary circuit to buy time and complete all the necessary drills, procedures and passenger briefings.
Prevention Strategies and Lines of Defense
Asked what they could have done better, the pilots commented as follows:
- The captain said he would have worked more to coordinate with the cabin crew and the passengers in the later stage of the final approach as he had done prior to the overflight, when he addressed the cabin twice.
- The first officer said he believed that he had been hindering the captain by thinking aloud rather than discussing plans of action in a more cohesive way. He believed thought processes should be organized so as to plan together and coordinate with the captain before carrying things out.
- The CRP thought that sticking to training was an ingredient for successful outcomes and that ATC coordination had also provided great assistance to help resolve the problem.
This situational example includes most of the lines of defense that would bring similar kinds of uncertain situations to a successful conclusion. The crew’s uncertainty over a successful outcome here had to do with the structural integrity of the airplane when coming to rest on the left engines. This was quickly resolved as the airplane proved to have plenty of momentum to stay on the runway, without any signs of breaking up when the left outboard engine settled onto the runway with only a slight wing down attitude. As a matter of fact, the right outboard engine touched the ground first, something the captain did not realize.
If an unexpected event occurs, the following are recommended for flight crews:
- Buy time to assess the situation.
- Build a common and consolidated understanding of the situation. Seek out all available information and do not hesitate to call for support.
- Maintain common situational awareness to improve judgment and subsequent decision making by:
- Continually evaluating the developing situation with conscious thinking and communication about the condition of the environment, the airplane, the pilots and the interactions occurring among the three.
- Anticipating the situation by asking “what if” questions such as what should be done if flight controls malfunction or two engines fail.
- Maintain cognitive flexibility, which means keeping an open mind to alternatives and other possibilities at all times.
- Work as a team and delegate or coordinate as much as possible to keep an overall picture of the situation.
Controllers should recognize that when faced with an emergency, the flight crew’s most important needs are time, airspace and silence on the frequency.
The controllers’ response could be patterned after the “ASSIST” memory aid:
- Acknowledge: Ensure that the reported situation is well understood and acknowledged.
- Separate: Establish and maintain separation with other traffic and terrain.
- Silence: Impose silence on your frequency and avoid disturbing urgent cockpit actions.
- Inform: Inform your supervisor and other sectors, units and airports, as appropriate.
- Support: Provide maximum support to the crew.
- Time: Allow the flight crew sufficient time to manage the situation.
The following are essential in bringing an emergency situation to a successful conclusion:
- Understand prevailing conditions before acting.
- Assess risks and time factors.
- Review and evaluate available options.
- Consider all implications before making a decision.
- Plan for contingencies.
- Create a shared problem model with other crewmembers by communicating.
- Match response to situation.
- Manage workload.
- Apply agreed action plans and monitor the results.
- Keep track of the essentials of the situation without getting carried away.
The crew’s professionalism was a major factor in this event. Professionalism is a blend of airmanship, common sense, Crew Resource Management, threat and error management (TEM), and many other ingredients that are part of proficiency and fitness for duty.
Associated OGHFA Material
Additional Reading Material
- Flight Safety Foundation Approach and Landing Accident Reduction (ALAR) Toolkit
- U.K. Civil Aviation Authority, SSL1, Good Airmanship Guide, 2000.