FlarePath

What happened

NTSB summary, verbatim

While configuring the airplane for landing, the left main landing gear light indicated that it was not down and locked. The flight crew accomplished the landing gear abnormal procedures, including recycling the landing gear once. The left main gear continued to indicate unsafe, and the captain landed the airplane. After touching down on the right main and the nose gear, the captain used right aileron to keep the left wing up as long as possible. The left wing eventually dropped to the runway and the airplane came to a stop at the runway’s left edge. During recovery of the airplane, the left main gear was partially extended, and no physical obstructions were observed that would prevent the gear from extending. Loosening a hydraulic line to the left main gear actuator allowed the gear to fall into the extended and locked position. The airplane was examined and the landing gear was cycled numerous times using the normal and alternate extension methods. The examination failed to duplicate the incident conditions; the gear extended and retracted normally without hesitation or binding. All major components of the main landing gear system, including the left main landing gear, left gear door, hydraulic pumps, valves and actuators were examined at the manufacturers’ facilities. Although some minor anomalies were noted, no evidence was found to explain the failure of the gear to extend. Analysis of fluid from the numbers 2 and 3 hydraulic systems revealed that the fluid exceeded the maximum particle contamination limits. The system 3 sample also contained metallic particles. Hydraulic system 3 powers gear extension and retraction. After the incident, the operator enhanced its maintenance procedures for testing hydraulic fluid to include contamination. The operator also added verbiage to its pilot procedures to further explain that, in certain cases, it is appropriate to make several attempts at normal gear extension and provided more explanation and guidance regarding the use of the back-up (freefall) system.

Photographs

9the aircraft, and what the investigators found

The aircraft before the accident

Wreckage and site documentation · 8 photographs from the docket

Photographs are NTSB docket attachments — works of the US government, in the public domain. Captions are the Board’s own.

Probable cause

the Board's determination

The failure of the left main landing gear to extend due to high levels of particulate contamination in the hydraulic fluid.

Occurrence sequence

1 stepsNTSB coding · CICTT taxonomy

1 · Landing-flare/touchdown
Landing gear collapse
defining event

Findings

2 causal · 0 contributing

CAUSE
Aircraft › Aircraft systems › Landing gear system › Main landing gear — Malfunction
CAUSE
Aircraft › Fluids/misc hardware › Fluids › Hydraulic fluid — Fluid condition

Sequence of events

6 timed eventsfrom the FDR factual report · claude-sonnet-5

N/ADescentp.4
Plot 1 covers the time from the beginning of the descent from 10,000' through the end of the recording and is a general overview of the last part of the flight.
N/AFinal approach/landingp.4
Plot 2 shows data from the last 50 seconds of the flight. The recording ended before the aircraft's airspeed dropped below 50 knots while the aircraft was still on the runway.
N/ALanding gear extension/retractionp.4
Plot 3 shows the timeframe when the landing gear was initially extended then retracted and extended again. The left main gear up and locked discrete indicated that the gear was up and locked when the nose and right gear were up and locked but the left gear down and locked discrete never indicated that the left gear was down and locked.
N/ALanding gear extension/retractionp.4
During the time when the nose and right landing gear were in the down and locked position a Gear Disagree warning was also indicated.
N/AEnd of recordingp.4
Parameters for DC Utility busses 1 and 2, DC Service Bus, and DC Essential Bus indicate that the busses went to the not powered state in the last recorded subframe; data may not be reliable as recorder was in the process of shutting down.
N/ALandingp.1
Aircraft landed with the left main landing gear retracted in Atlanta, Georgia.

NTSB analysis

from the final report

While configuring the airplane for landing, the left main landing gear light indicated that it was not down and locked. The flight crew accomplished the landing gear abnormal procedures, including recycling the landing gear once. The left main gear continued to indicate unsafe, and the captain landed the airplane. After touching down on the right main and the nose gear, the captain used right aileron to keep the left wing up as long as possible. The left wing eventually dropped to the runway and the airplane came to a stop at the runway’s left edge. During recovery of the airplane, the left main gear was partially extended, and no physical obstructions were observed that would prevent the gear from extending. Loosening a hydraulic line to the left main gear actuator allowed the gear to fall into the extended and locked position. The airplane was examined and the landing gear was cycled numerous times using the normal and alternate extension methods. The examination failed to duplicate the incident conditions; the gear extended and retracted normally without hesitation or binding. All major components of the main landing gear system, including the left main landing gear, left gear door, hydraulic pumps, valves and actuators were examined at the manufacturers’ facilities. Although some minor anomalies were noted, no evidence was found to explain the failure of the gear to extend. Analysis of fluid from the numbers 2 and 3 hydraulic systems revealed that the fluid exceeded the maximum particle contamination limits. The system 3 sample also contained metallic particles. Hydraulic system 3 powers gear extension and retraction. After the incident, the operator enhanced its maintenance procedures for testing hydraulic fluid to include contamination. The operator also added verbiage to its pilot procedures to further explain that, in certain cases, it is appropriate to make several attempts at normal gear extension and provided more explanation and guidance regarding the use of the back-up (freefall) system.

BOMBARDIER INC CL-600-2B1Atlantic Southeast Airlines