Landing Gear Problems: Guidance for Controllers
Landing Gear Problems: Guidance for Controllers
Description
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.
Effects
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
On 29 September 2019, an Airbus A330-200 received simultaneous indications of low pressure in two hydraulic systems soon after takeoff. An emergency was declared, and a return to land was followed by a stop on the runway due to a burst main wheel tyre. A manual valve for one of the hydraulic systems located in the left main gear wheel well had completely detached and impact-damaged a pipe in a nearby but separate hydraulic system. Both systems lost their fluid with valve detachment attributed to fatigue failure of the attachment screws, a risk addressed by an un-adopted non-mandatory Service Bulletin.
On 18 June 2021, a Boeing 787-8 being operated by British Airways was being loaded for a cargo flight at Heathrow whilst line engineering carried out checks required to permit despatch with a deferred minor defect for later rectification. The check required cycling the landing gear with locking pins inserted so that only the bay doors cycled but when this was done, the nose gear retracted and the front of aircraft dropped to the ground causing significant damage to the airframe and minor injuries to two people. The nose gear downlock pin had inadvertently been inserted into the wrong hole.
On 3 December 2021, a Boeing 737MAX-8 released to service with antiskid and autobrake systems inoperative in accordance with Minimum Equipment List procedures then operated two sectors. On the return to Singapore, both left main landing gear tyres were sufficiently damaged during landing to cause the bursting of one and deflation of the other. The cause of this was failure to deploy the speedbrakes manually as required. A similar error on the previous sector did not have the same outcome because the relatively more positive touchdown enabled automatic speedbrake deployment and wheel spin was accompanied by simultaneous manual braking.
On 7 June 2021 an Embraer ERJ170 had just commenced its descent towards destination when both primary and secondary pitch trim systems failed resulting in excessive nose-down pitch control forces and an inoperative autopilot. The flight was completed without further event with the Pilot Flying using both hands on the control yoke to control pitch attitude manually. During the landing roll the nosewhweel steering system also failed. The pitch trim failure was attributed to probable jamming of the trim actuator due to water, possibly condensation, freezing within it. The steering system fault was attributed to a completely unrelated sensor failure.
On 6 August 2021, an Airbus A319 experienced uncommanded loss of both Flight Directors and the Flight Mode Annunciator and disconnection of both autopilot and autothrust in the climb. After levelling at FL350, significant inertial reference position inconsistencies were observed. A precautionary PAN was declared and the flight was completed. Investigation found that the cause was a momentary abnormal vertical shock load transferred to Inertial Reference System equipment through an overextended nose gear shock absorber by a sharp jolt during takeoff caused by a runway patch repair. Sensitivity of the particular inertial reference system installed on the aircraft was noted.
Further Reading
EUROCONTROL
- Guidelines for Controller Training in the Handling of Unusual/Emergency Situations
- ATC Refresher Training Manual, ed.1.0, March 2015
UK CAA
