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Cases › LAX05IA312 · Part 121 airline

Airbus Industrie A320Jet Blue Airways, Inc.

Los Angeles, CA, USA · 2005-09-22·N536JB

0
fatal
0
serious
No injury
highest injury
Minor
damage
Replay the flight data11,001 samples · 17 parametersSRN 180,500 – SRN 191,500Replay the flight data31 samples · 12 parametersSRN 177,975 – SRN 178,005Replay the flight data31 samples · 12 parameters42:49:00.0 – 42:49:30.0Replay the flight data121 samples · 13 parameters37:39:30.0 – 37:41:30.0AnalyseThe analystOne timeline · precedents · ask the docket · what the record saysGenerateInvestigation briefFacts, cause, recorder extremes, sequence, sourcesSourceNTSB docket19 documents on data.ntsb.gov

What happened

NTSB summary, verbatim

Shortly after the landing gear handle was positioned to the up position in the initial climb, the flight crew noted an error message on the Electric Centralized Aircraft Monitoring (ECAM) system listing a fault (L/G SHOCK ABSORBER FAULT) message for the nose landing gear (NLG) shock absorber. The gear handle was then moved to the down position and the crew received an error message of a fault for the nose wheel steering (WHEEL N/W STRG FAULT). After determining that the nose landing gear was cocked 90 degrees, the crew landed at an alternate airport, and the NLG tires and both wheels were worn down into the axle. Post incident examination of the nose gear assembly found that two of the four anti-rotation lugs on the NLG upper support assembly fractured and separated due to induced fatigue from the stearing system's programed pre-landing dynamic steering tests that repeatedly cycles pressure to the stearing cylinders. The failed lugs allowed the NLG to deviate from its 0-degree position in the landing gear bay upon gear retraction on takeoff. This resulted in the L/G SHOCK ABSORBER FAULT error message on the ECAM system. When the pilots extended the incident airplane's landing gear, the nose gear achieved the down and locked position 1.5 seconds before the main gear and/or all of the landing gear doors closed. The nose wheel assembly was not centered at this time. The Brake Steering Control Unit (BSCU) detected this off center condition of the NLG and attempted to re-center the nose wheel; however, due to the sequencing of the nose and main landing gear and their respective doors, hydraulic pressure was shut off to the NLG steering valve. This lack of hydraulic power to the servo valve resulted in a lack of position feedback to the BSCU. After a 0.5-second monitoring time period, the BSCU detected this as a fault and deactivated the steering system so that the BSCU could not return the nose wheels to center. Failure of the nosewheels to center initiated a WHEEL N/W STRG FAULT caution message on the ECAM. There were no approved procedures that allowed the flight crew to attempt to reset the BSCU system, which would have re-enabled the hydraulic system and could have resulted in the system recentering the nose wheels.

Photographs

34the aircraft, and what the investigators found
Wreckage and site documentation · 34 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 fatigue failure of two anti-rotation lugs due to repeated cyclic pre-landing tests, which allowed the nosewheels to deviate from the 0-degree position on landing gear retraction. A contributing factor was the design of the Brake Steering Control Unit (BSCU) system logic, which prevented the nosewheels from centering. Also contributing was the lack of a procedure to attempt to reset the BSCU system under these conditions.

Sequence of events

16 timed eventsfrom the FDR factual report · claude-sonnet-5
  1. SRN 180949Departure/gear retractionp.3
    Nose gear squat switch indicated 'air'; right landing gear squat switch indicated 'air' two seconds later, followed by left landing gear squat switch the following second
  2. few seconds after SRN 180949Departure/gear retractionp.3
    Gear Selector Down changed from 'Selector Down' to 'Selector Not Down'; Gear Selector Up changed from 'Selector Not Up' to 'Selector Up' at about the same time
  3. SRN 180960Departure/gear retractionp.3
    Gear Down Locked changed from 'Down Locked' to 'Not Locked Down.' Six seconds later, Gear Up Locked changed from 'Not Locked Up' to 'Locked Up.'
  4. SRN 180974In flightp.3
    Nose gear squat switch indicated 'ground' for about 11 seconds (25 seconds after first indicating 'air'), then returned to 'air' for 2 seconds before indicating 'ground' for the remainder of the flight
  5. over a minute after SRN 180974 sequenceIn flightp.3
    Gear Down Locked changed to 'Down Locked' and Gear Up Locked changed to 'Not Locked Up' and remained in those states for the rest of the flight
  6. SRN 191032Landingp.4
    Initial touchdown occurred when the left and right landing gear squat switches indicated 'ground'
  7. SRN 191040Landing rolloutp.4
    The airplane began a slight longitudinal deceleration
  8. SRN 191050Landing rolloutp.4
    There was a drop in vertical acceleration to 0.719 g's
  9. SRN 191060Landing rolloutp.4
    Significant longitudinal deceleration began with an airspeed of 96.8 knots
  10. SRN 191082Landing rolloutp.4
    Longitudinal deceleration ended
  11. SRN 177993Previous landing (Burbank) - for comparisonp.4
    The left and right landing gear squat switches indicated 'ground.' The nose gear squat switch indicated 'ground' the following second (previous landing at Burbank)
  12. SRN 135578Previous takeoff - for comparisonp.4
    Nose gear squat switch indicated 'air.' The left and right landing gear squat switch indicated 'air' three seconds later (third previous takeoff)
  13. SRN 135582Previous takeoff - for comparisonp.4
    Gear Selector Up changed from 'Selector Not Up' to 'Selector Up'
  14. SRN 135584Previous takeoff - for comparisonp.4
    Gear Selector Down changed from 'Selector Down' to 'Selector Not Down.' The nose gear squat switch indicated 'ground' at this time
  15. SRN 135676Previous takeoff - for comparisonp.4
    Gear Selector Down changed from 'Selector Not Down' to 'Selector Down.' Two seconds later Gear Selector Up changed from 'Selector Up' to 'Selector Not Up'
  16. SRN 135682Previous takeoff - for comparisonp.4
    The nose gear squat switch indicated 'air' and remained in that status for the rest of the flight

NTSB analysis

from the final report

Shortly after the landing gear handle was positioned to the up position in the initial climb, the flight crew noted an error message on the Electric Centralized Aircraft Monitoring (ECAM) system listing a fault (L/G SHOCK ABSORBER FAULT) message for the nose landing gear (NLG) shock absorber. The gear handle was then moved to the down position and the crew received an error message of a fault for the nose wheel steering (WHEEL N/W STRG FAULT). After determining that the nose landing gear was cocked 90 degrees, the crew landed at an alternate airport, and the NLG tires and both wheels were worn down into the axle. Post incident examination of the nose gear assembly found that two of the four anti-rotation lugs on the NLG upper support assembly fractured and separated due to induced fatigue from the stearing system's programed pre-landing dynamic steering tests that repeatedly cycles pressure to the stearing cylinders. The failed lugs allowed the NLG to deviate from its 0-degree position in the landing gear bay upon gear retraction on takeoff. This resulted in the L/G SHOCK ABSORBER FAULT error message on the ECAM system. When the pilots extended the incident airplane's landing gear, the nose gear achieved the down and locked position 1.5 seconds before the main gear and/or all of the landing gear doors closed. The nose wheel assembly was not centered at this time. The Brake Steering Control Unit (BSCU) detected this off center condition of the NLG and attempted to re-center the nose wheel; however, due to the sequencing of the nose and main landing gear and their respective doors, hydraulic pressure was shut off to the NLG steering valve. This lack of hydraulic power to the servo valve resulted in a lack of position feedback to the BSCU. After a 0.5-second monitoring time period, the BSCU detected this as a fault and deactivated the steering system so that the BSCU could not return the nose wheels to center. Failure of the nosewheels to center initiated a WHEEL N/W STRG FAULT caution message on the ECAM. There were no approved procedures that allowed the flight crew to attempt to reset the BSCU system, which would have re-enabled the hydraulic system and could have resulted in the system recentering the nose wheels.