Aircraft Accidents and Lessons Unlearned XLIII: JetBlue Airways Flight 292

JetBlue flight 292 during emergency landing in Los Angeles airport

On September 21, 2005, JetBlue Airways, registration number N536JB, flight 292 landed at Los Angeles International Airport (LAX) with its nose gear wheel turned ninety degrees from center. The Airbus A320 departed Burbank airport headed for JFK airport in New York. The flight crew flew the aircraft for close to three hours to burn off fuel for the emergency landing; the decision to divert was made after the unsuccessful retraction of the nose landing gear (NLG) because the NLG tires blocked the gear from folding into the wheelwell. The two main gears, meanwhile, operated normally.

National Transportation Safety Board (NTSB) accident investigation, LAX05IA312, did not go through the normal investigatory process – it is assumed – because there were no casualties; the aircraft was not destroyed. As soon as the media blitz ended, complete with helicopter vantage point coverage of the edge-of-one’s-seat landing, the accident was put to the back pages. This was an unfortunate mistake; an aircraft that survived an accident would have been a teaching tool like no other. Six years earlier, a US Airways Airbus A320, flight 1549, survived its accident mostly intact. However, just like JetBlue 292, the NTSB missed important information in that accident and then failed to follow up on crucial findings that were instrumental to the industry.

The report was confusing; the terminology was ambiguous. Because of Airbus’s excessive use of sensors in the NLG steering and positioning, the reader, in order to understand what was happening, should have had a better narrative. For instance, when describing the proximity sensors, the report states, “There are a pair of proximity sensors and targets on the NLG that detect if the gear is extended (airplane in air) or if the gear is compressed (airplane on the ground).” When a gear is deployed in flight, it is considered ‘extended’, ‘retracted’ when up in the well. Instead, the report used ‘extended’ to describe the strut as extended, not the gear. Also, the ambiguous use of, “… a pair of proximity sensors and targets …” does nothing to aid understanding of what sensors/targets, how many sensors/targets are used, when during the deploy sequence are they required and for what purpose.

In 1966, Star Trek (the original series) relied heavily on storyline, not limited technology computer graphics (CG) to be successful. Common sense overrode technology. In contrast, 2017’s Star Trek: Discovery relied heavily on CG – not storyline. Technology replaced common sense. The successful franchise wasn’t broken, so why did they ‘fix’ it?

Today, technology has become the digital aircraft’s prominent characteristic, while reliable decades-old technologies are dismissed. The extensive use of technology does not make aircraft systems unsafe – it makes the systems unpredictable. For instance, the JetBlue 292 accident report mentioned that the A320 employs a device called the Brake Steering Control Unit (BSCU); it electronically controls the aircraft’s steering system. One BSCU function is to perform four bite tests – four deflections of the NLG steering through five degrees of travel … left to right … in flight … before touchdown. Why? Why test the steering before landing? Could this bite test have contributed to JetBlue 292’s misaligned nose strut?

Before digital wire technology, steering was simple; it was accomplished via a series of cables, pulleys and bellcranks. The steering system was not heavy because it ran from the NLG to the Captain’s steering tiller directly above. This system always worked; there was no need to test the steering in flight. The fundamental steering system design wasn’t broke – why fix it? Airbus, by employing numerous sensors and targets, ‘corrected’ a system that worked; they fixed the system beyond all repair.

Meanwhile, NTSB investigators were so caught up with the technology, that they forgot to check a most important factor: Was the NLG strut properly serviced? The gear’s integrity was intact – the strut, uncompromised; they could have checked. The NTSB docket for LAX05IA132 had nineteen specialty reports and documents; not one answered the simple question of strut servicing. The JetBlue 292 accident report did not answer that question either. Why, then, is strut servicing important?

NLGs, since the dawn of tricycle gear use (a nose gear and two mains) have used a mechanical device called the centering cam. The NLG shock strut has three main parts: a piston (chrome strut), an upper cylinder body (the sleeve the piston slides in; it connects to the aircraft) and the scissor links, which, among other things, prevent separation of the piston and cylinder body. Centering cams, also called locating cams, are mechanical devices located inside the strut. A locating cam (LC) is a simple design; each pair resemble two sine waves that slide together when employed. There are two LCs: an upper and a lower. As the aircraft rotates, weight comes off the NLG. The strut’s nitrogen pneumatic charge immediately pushes the piston away from the upper cylinder body. The upper LC on the piston engages the lower LC attached to the cylinder body, which aligns the gear to the aircraft centerline. Simple.

The A320 has centering cams. They work … but only as long as the strut is properly serviced with nitrogen to force the upper and lower LCs to engage. The accident report did not verify JetBlue 292’s NLG had the proper nitrogen charge. The centering cams would have made the sensor/target technology irrelevant in lining up the NLG to the centerline. Was the NLG strut properly serviced?

Unfortunately, in its inexperience, the NTSB did not understand this. Instead, they focused on cracks found on the NLG’s upper support assembly’s four lugs; damage from NLG stresses during landing. The four lugs did not contribute to the gear strut turning ninety degrees from the centerline, so this begs the question: Who cares? Why examine damage made after the landing? The purpose of an accident report is to highlight the cause(s) that led to the accident, not what was incurred after.

Furthermore, the NTSB spent great effort analyzing sensors and targets that – maybe – contributed to the accident yet did not produce a viable solution to any problems they may have caused. To slightly alter an Abba Eban quote, “The [NTSB] never misses an opportunity to miss an opportunity.”

Here are two examples of why maintenance-experienced investigators – specifically, airframe and powerplant certificated maintenance investigators with experience working in the industry – are critical to the NTSB investigatory process. First, a practical problem: It appears (because the NTSB did not provide NLG strut servicing evidence) that important clues were missed prior to flight. Was the strut ‘showing chrome’; in other words, was the strut flat, deflated, not serviced properly? This would have been caught by (hopefully) two individuals: the mechanic assigned to the flight and the first officer during his/her preflight walkaround. A flat strut would have been evidence of the strut requiring servicing or a leak. If the strut was properly serviced, again, the inflight emergency may not have happened. This would amount to an operational problem at JetBlue, a procedural revision of their manuals.

Second, a technical problem. The NTSB identified an unknown number of sensors and targets that track just the NLG’s movements, such as deployment, retraction, inflight steering tests, up-and-locked or down-and-locked. The consequence of the technology, as stated, “… a failure condition can exist that results in the NLG system sensing ‘ground/compressed’ when the gear is extended and a mechanical failure allows the NLG wheel to rotate to a position greater than 6 degrees.” The report confused ‘extended’ with down-and-locked/ strut at full travel; the “NLG wheel to rotate” should have been written “strut turned – or steered –  to a position greater than 6 degrees”. One can see how JetBlue 292’s strut turned ninety degrees from centerline; the still rotating wheels caused vibrations that helped the airstream turn the strut beyond the allowable six degrees in a few seconds.

With numerous sensors and targets, Airbus created multiple-point failure opportunities. There are too many sensors and targets, which lead to: (1) countless chances for computer error, and (2) numerous occasions for these sensors/targets to become damaged in day-to-day use, which, again, leads to computer error. The fact that the strut was able to rotate beyond six degrees should have raised multiple flags. It should have caught an experienced eye and acted on.

No accident, whether survivable or not, is too small or insignificant. What information was lost and could have been learned by JetBlue 292 cannot be emphasized enough. Investigations large and small demand qualified investigators that can identify problems and fix them. The traveling public deserve better.

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