This article provides guidance for tower/approach controllers on what to expect from an aircraft experiencing the effects of landing gear problems and some of the considerations which will enable the controller, not only to provide as much support as possible to the aircraft concerned, but also maintain the safety of other aircraft at or in the vicinity of an aerodrome and of the ATC service provision in general.
Useful To Know
Fixed, non-retractable landing gear was common in the early days of aviation but is now only seen on light aircraft. Commercial airliners use complex retractable undercarriages with multi-step automated retraction and extension sequences, and various systems to provide status information, redundancy and control. One such system provides easily interpretable indicator lights to provide the positional status of the landing gear. The principle is simple - a green light when the landing gear is down and locked and a red light when there is a discrepancy between the gear lever and landing gear positions. The unsafe indication might be the first sign of a problem related to the proper preparation of the landing gear for landing. Depending on the aircraft type and landing gear retraction system, the exact nature of the problem may vary significantly.
Fuel consumption, with High Lift Devices (flaps and slats) deployed and landing gear either fully or partially extended, is significantly higher than is the case when the aircraft is in a "clean" configuration. Flight Management System (FMS) fuel predictions are usually not accurate when the aircraft is not in the "normal" configuration for the phase of flight.
Due to the variety of modern aircraft landing gear design, it could be quite difficult for a non-professional to distinguish between normal and abnormal gear operation. In the case of a partial extension, any visual inspection should be done only by a qualified professional.
Landing with main/nose gear that might not be locked/fully extended could result in:
- Gear-up landing;
- Landing with partially extended undercarriage;
- Gear collapse with subsequent airframe damage.
All of the above could by followed by runway excursion and post-crash fire.
Anticipated Impact on Crew
In case of a gear problem, the crew bears significant stress. They will need time to fully assess the nature of the problem. Further steps could include crew visual inspection (depending on aircraft design), alternate extension procedures which may include manual emergency landing gear extension, or flight manoeuvres designed to force the drop of the landing gear. All of these steps require significant preparation.
It might be necessary to perform several low pass approaches in order for qualified technical personnel to inspect visually the landing gear status and position.
A landing with confirmed unlocked gear could result in an emergency evacuation of the aircraft and the cabin crew will need to prepare the cabin and passengers for such an event.
For further information, see the separate article: "Landing Gear Problems: Guidance for Flight Crews"
Suggested Controller's Actions
Best practice embedded in the ASSIST principle could be followed: (A - Acknowledge; S - Separate, S - Silence; I - Inform, S - Support, T - Time)
A - acknowledge the gear problem, ask for the crews’ intentions when the situation permits, and establish whether the crew is able to extend the gear into locked position. Dtermine the number of souls on board (SOB); determine the aircraft fuel on board and endurance in minutes. Update the endurance value as appropriate to the situation but at least every 15-20 minutes to help reduce the potential for a fuel emergency (if the gear problem arises during approach the controllers may expect the declaration of minimum fuel or even an impending fuel emergency very soon as it may be very common today to arrive with less than 10 minutes of extra fuel in excess of minimum diversion fuel at the destination);
S - separate the aircraft from other traffic, prioritise it for landing (allow long final if requested), keep the active runway clear of departures, arrivals and vehicles;
S - silence the non-urgent calls (as required) and use separate frequency where possible;
I - inform the airport emergency services and all concerned parties according to local procedures;
S - support the flight experiencing gear problems with any information requested and deemed necessary (e.g. type of approach, runway length and aerodrome details, etc.);
T - provide time for the crew to assess the situation, don’t press with non urgent matters.
What to Expect
If a crew has declared gear problems, the controller may anticipate:
- Need for time to resolve the exact nature of the problem;
- Holding pattern request for preparation and execution of manual gear extension;
- The necessity of time and place to perform specific manoeuvres with the purpose of full extension;
- One or multiple low passes for visual inspection;
- Low speed approach;
- Need for rescue and fire services to be on standby;
- Runway blockage after landing;
- Diversion of the affected flight to an airfield with a longer runway;
- Declaration of an emergency both due to the gear problems and/or low fuel situation;
- Lateral runway excursion (in case of landing with gear extended only partially or in case of sudden gear failure after touchdown);
- Aircraft Evacuation.
What to Provide
Apart from the above mentioned, a controller should:
- Transfer affected aircraft to another frequency, if applicable;
- Maintain close coordination with ground emergency units - an early call could facilitate more effective deployment of resources;
- Maintain awareness of the aircraft fuel endurance - provide reminders to the crew if required
- Have direct contact with aircraft operator’s technical representative (if possible) - any result of a visual inspection should be passed to the crew without delay.
- Be prepared to provide a wider range of information to the crew on request.
- DO NOT certify the down and locked position of the landing gear - visual inspection during low pass should be done by qualified personnel. If not possible, the tower controller should provide information about landing gear not extended or only partly extended to the aircraft concerned without delay.
- Use the proper phraseology as recommended by ICAO for such events, i.e. “The landing gear appears down” and “Landing gear appears up”. Useful phraseology utilised for such events is included in ICAO Doc 9432 Manual of Radiotelephony, Chapter 4, item 4.7.3, which states:
"If the low pass is made for the purpose of observing the undercarriage, one of the following replies could be used to describe its condition (these examples are not exhaustive):
- landing gear appears down;
- right (or left, or nose) wheel appears up (or down);
- wheels appear up;
- right (or left, or nose) wheel does not appear up (or down)."
Accidents and Incidents
- A320, Los Angeles USA, 2005: On 21 September 2005, an Airbus A320 operated by Jet Blue Airways made a successful emergency landing at Los Angeles Airport, California, with the nose wheels cocked 90 degrees to the fore-aft position after an earlier fault on gear retraction.
- A310, Vienna Austria, 2000: On 12 July 2000, an Airbus A310 being operated by Hapag Lloyd on a non scheduled passenger flight from Chania to Hannover declared an emergency due to fuel shortage and, after making an en route diversion to Vienna in day VMC, crash landed short of runway 34.
- DH8D, Aalborg Denmark, 2007: On 9 September 2007 the crew of an SAS Bombardier DHC8-400 approaching Aalborg were unable to lock the right MLG down and prepared accordingly. During the subsequent landing, the unlocked gear leg collapsed and the right engine propeller blades struck the runway. Two detached completely and penetrated the passenger cabin injuring one passenger. The Investigation found that the gear malfunction had been caused by severe corrosion of a critical connection and noted that no scheduled maintenance task included appropriate inspection. A Safety Recommendation to the EASA to review the design, certification and maintenance of the assembly involved was made.
- A343, London Heathrow UK, 1997: On 5 November 1997, an Airbus A340-300 operated by Virgin Atlantic airlines experienced a landing gear malfunction. The crew executed a successful partial gear up landing at London Heathrow.