Over a decade since a fatal Bombardier Learjet 60 overrun in South Carolina, operators of the type are being ordered to install a voice-command warning system to alert pilots to thrust-reverser malfunctions.
The aircraft, operated by Global Exec Aviation, had been departing for Van Nuys from runway 11 at Columbia Metropolitan airport.
But the aircraft’s main-gear tyres, which were badly under-inflated, burst during the take-off roll and – although the jet was beyond the V1 decision speed – the crew attempted to abort.
Although the crew deployed the thrust-reversers, the landing-gear damage interfered with the air-ground system logic, causing uncommanded stowing of the reversers after their deployment – effectively resulting in thrust from the engines accelerating the aircraft forward.
The Learjet overran and was destroyed by fire, fatally injuring both pilots and two of the four passengers.
Under a new directive, effective 25 June, the US FAA is ordering installation of a voice-command warning system to “mitigate” failure of the reverser system by alerting the crew.
It says the modification needs to be carried out within two years or 1,200h in service.
The National Transportation Safety Board had issued a recommendation in July 2009, about 10 months after the September 2008 accident, that Learjet should install improved aural or visual cues on the aircraft to allow pilots to recognise inadvertent reverser stowage.
Despite more than a decade passing since the accident and the recommendation, the FAA has declined an NTSB request to shorten the compliance time.
The FAA says it “considered the urgency” of the unsafe condition and the “practical aspects” of achieving the modification within a period that aligns with most operators’ normal maintenance schedules.
It also rejected a request, from a separate commenter, to withdraw the directive for reasons that aircraft designs have moved away from using multitudes of aural warnings.
The FAA says the change incorporates a “direct aural voice command for a rapid effective response” and will “prevent” scenarios similar to the Columbia Learjet 60 accident.
Investigators had criticised both Learjet’s and the FAA’s safety analysis for the aircraft and the decision to certify the type, in 1993, to some standards which applied to the original Learjet 24 model in 1966.
This decision “allowed for deficiencies” which would “not likely” have been present if updated regulations had been applied.
The inquiry also expressed concern over modifications introduced after a previous thrust-reverser accident, which occurred to a Learjet 60 landing at Troy, Alabama, in January 2001.
It found that Learjet’s analysis and the FAA’s review of the modification were inadequate and did not address design deficiencies, pointing out that a crew procedure – rather than a design change – was initially introduced to mitigate the “serious” hazard of uncommanded forward thrust, and that a subsequent supplementary design change also failed to address the problem.