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Cases › DCA13FA094 · Part 121 airline

BOMBARDIER DHC8Piedmont Airlines

Newark, NJ, USA · 2013-05-18·N934HA

0
fatal
0
serious
No injury
highest injury
Substantial
damage
Replay the flight data7,871 samples · 9 parameters22:51:01.0 – 25:02:12.0AnalyseThe analystOne timeline · precedents · ask the docket · what the record saysGenerateInvestigation briefFacts, cause, recorder extremes, sequence, sourcesSourceNTSB docket15 documents on data.ntsb.gov

What happened

NTSB summary, verbatim

While on an instrument approach to the airport, when the flight crew attempted to lower the landing gear, they received an unsafe indication on the left main landing gear (MLG). They conducted a fly by of the airport control tower, and the controller verified that the left MLG was only partially extended. The flight crew performed the alternate landing gear extension procedure and worked with company maintenance to troubleshoot the failure, however, the left MLG would not extend after multiple attempts.  Although the first officer indicated that he became confused after the sixth step of the alternate landing gear extension procedure, post accident testing determined that this did not have any effect on the outcome  Because the left MLG would not extend, the captain elected to conduct the landing with all gear retracted to minimize the likelihood of a loss of directional control after touchdown. All passengers and crew successfully evacuated after the airplane came to a rest on the runway. Postaccident testing confirmed that the left MLG would not deploy using the normal or alternate gear extension systems.  Examination of the landing gear components found that the left MLG uplock roller was seized and the groove on the left uplock latch was out of tolerance. The seized uplock roller and worn latch caused the forces to exceed the crews capability to release the landing gear by use of the alternate gear extension system. Examination of the operators maintenance records indicated that the uplock rollers were to be inspected every 220 flight hours and that they were to be lubricated only on condition.  The accident airplanes left MLG uplock was inspected 11 times in year prior to the accident. In all instances, the inspection paperwork indicated that the roller rotated freely and did not require lubrication for the last. Further, the uplock latches were to be visually inspected every 440 flight hours.  The latches were not required to be measured and were replaced only on condition.  The last measurement of the left MLG latch on the accident airplane occurred 10 years prior to the accident. After the accident, the operator modified the maintenance procedures to include regular lubrication of the rollers and to measure the wear of the uplock latch. 

Probable cause

the Board's determination
the frozen left main landing gear (MLG) uplock roller due to lack of lubrication and the uplock latch that had worn beyond acceptable tolerances, which prevented the flight crew from extending the left MLG using the alternate extension system. Contributing to the accident were the operator's improper maintenance practices, which did not detect the lubrication issue with the roller and the wear of the latch.

Occurrence sequence

2 stepsNTSB coding · CICTT taxonomy
  1. 1 · Approach
    Sys/Comp malf/fail (non-power)
  2. 2 · Landing-landing roll
    Abnormal runway contact
    defining event

Findings

2 causal · 0 contributing
  • CAUSE
    Aircraft › Aircraft systems › Landing gear system › Main landing gear — Malfunction
  • CAUSE
    Organizational issues › Management › Policy/procedure › Adequacy of policy/proc — Operator

Sequence of events

11 timed eventsfrom the FDR factual report · claude-fable-5-1 (in-session)
  1. 23:05:22 EDT (May 17)takeoffp.3
    Takeoff
  2. 23:12:38 EDTcruisep.3
    Aircraft leveled at an average pressure altitude of 6,800 ft
  3. 23:27:42 EDTdescentp.3
    Descent to land began
  4. 23:30:52 EDTgo-aroundp.3
    Go-around on final approach, pitching to 9 degrees and climbing to a pressure altitude of 2,800 ft
  5. 00:04:42 EDT (May 18)approachp.3
    After holding about 2,800 ft, the aircraft began descending for another approach
  6. 00:12:21 EDTgo-aroundp.3
    Second go-around: pitched up to 11 degrees and climbed back to about 2,800 ft
  7. 00:32:20 EDTholdingp.3
    First vertical g maneuver reaching 1.6 g (attempt to lower the left main gear)
  8. 00:32:52 EDTholdingp.3
    Second vertical g maneuver reaching 1.4 g
  9. 00:57:58 EDTapproachp.3
    Aircraft began the landing descent from 2,600 ft
  10. 01:01:51 EDTlandingp.3
    During the gear-up landing, high excitations in the accelerations began to build; airspeed dropped from about 81 knots to a final value of 58 knots
  11. 01:02:03 EDTlandingp.3
    Power removed from the FDR

NTSB analysis

from the final report

While on an instrument approach to the airport, when the flight crew attempted to lower the landing gear, they received an unsafe indication on the left main landing gear (MLG). They conducted a fly by of the airport control tower, and the controller verified that the left MLG was only partially extended. The flight crew performed the alternate landing gear extension procedure and worked with company maintenance to troubleshoot the failure, however, the left MLG would not extend after multiple attempts.  Although the first officer indicated that he became confused after the sixth step of the alternate landing gear extension procedure, post accident testing determined that this did not have any effect on the outcome  Because the left MLG would not extend, the captain elected to conduct the landing with all gear retracted to minimize the likelihood of a loss of directional control after touchdown. All passengers and crew successfully evacuated after the airplane came to a rest on the runway. Postaccident testing confirmed that the left MLG would not deploy using the normal or alternate gear extension systems.  Examination of the landing gear components found that the left MLG uplock roller was seized and the groove on the left uplock latch was out of tolerance. The seized uplock roller and worn latch caused the forces to exceed the crews capability to release the landing gear by use of the alternate gear extension system. Examination of the operators maintenance records indicated that the uplock rollers were to be inspected every 220 flight hours and that they were to be lubricated only on condition.  The accident airplanes left MLG uplock was inspected 11 times in year prior to the accident. In all instances, the inspection paperwork indicated that the roller rotated freely and did not require lubrication for the last. Further, the uplock latches were to be visually inspected every 440 flight hours.  The latches were not required to be measured and were replaced only on condition.  The last measurement of the left MLG latch on the accident airplane occurred 10 years prior to the accident. After the accident, the operator modified the maintenance procedures to include regular lubrication of the rollers and to measure the wear of the uplock latch.