The European Union Aviation Safety Agency (EASA) has published a Proposed Airworthiness Directive (PAD) , signalling its intention to approve the Boeing 737 MAX’s return to Europe’s skies “within a matter of weeks” – probably about mid-January.
But Europe is specifying a few requirements that the US Federal Aviation Administration (FAA) has not demanded.
It was on 20 November that the FAA approved the aircraft’s return to America’s skies, but US carriers have many preparations to complete before resuming commercial services with the Max. American Airlines reckons it will be ready by the end of December.
EASA, however, wants to see the application of some operational measures that the FAA does not require. It insists, nevertheless, that the Max airframes in America and in Europe will be the same. The agency explains: “The [PAD] requires the same changes to the aircraft as the FAA, meaning that there will be no software or technical differences between the aircraft operated by the United States operators and by the EASA member states operators.”
The EASA PAD is a consultation document, and all responses have to be received by 22 December. EASA executive director Patrick Ky is at pains to point out that the agency, while cooperating with the FAA on correcting the anomalies in the Max’s manoeuvring characteristics augmentation system (MCAS) (see immediately preceding blog entry), insisted on looking independently at the whole issue.
Ky explained: “EASA’s review of the 737 MAX began with the MCAS but went far beyond. We took a decision early on to review the entire flight control system and gradually broadened our assessment to include all aspects of design which could influence how the flight controls operated. This led, for example, to a deeper study of the wiring installation, which resulted in a change that is now also mandated in the [PAD].” That, basically, is a requirement to bring the venerable 737’s design up to date, and is a signal that the days of “grandfather rights” – a dispensation to build the 737 Max as earlier versions of the 737 were constructed rather than as new aircraft have to be designed – are numbered.
The Max airframe design came through all the handling tests satisfactorily, as Ky explained: “We also pushed the aircraft to its limits during flight tests, assessed the behaviour of the aircraft in failure scenarios, and could confirm that the aircraft is stable and has no tendency to pitch-up even without the MCAS.”
Two principle differences between the FAA and EASA requirements are explained as follows: “EASA explicitly allows flight crews to intervene to stop a stick-shaker from continuing to vibrate once it has been erroneously activated by the system, to prevent this distracting the crew. EASA also, for the time being, mandates that the aircraft’s autopilot should not be used for certain types of high-precision landings [and approaches such as RNP-AR]. The latter is expected to be a short-term restriction.”
The crew intervention mentioned would allow the pilots to pull the stick-shaker circuit breaker. The stick-shaker – a system designed to alert pilots to an approaching stall – was one of the distractions that faced the Lion Air and Ethiopian Airlines crews before they lost control of their aircraft, despite the fact that the shaker was triggered by a false warning.
The FAA doesn’t see the need for this intervention, because the modifications have ensured that a single sensor failure will not trigger the stick-shaker any more.
Boeing and EASA say they have agreed to continue tests to see if they can further strengthen the aircraft’s systems’ resilience to angle of attack (AoA) sensor failures – the causal trigger for the two fatal Max accidents, and Boeing has also made this promise: “Boeing will also conduct a complementary Human Factor assessment of its crew alerting systems within the next 12 months, with the aim of potentially upgrading these to a more modern design approach.”