The FAA has formally ungrounded the Boeing 737 MAX but it’s going to be some time before we see the aircraft back in the sky in the numbers we are used to. It’s been 20 months since the grounding occurred and the focus now shifts to airlines, in terms of who will be first? It’s likely to be a US operator, but it’s simply a case of is there the passenger demand to fill the seats on these aircraft returning to the ramp?

If there is, operators are going to have to ensure that each MAX undergoes an Operational Readiness Flight, according to Service Bulletin 737-00-1028. Due to the complex nature of the grounding, this will be far more complicated, than normal with a multitude of additional procedures needing to be signed and certified.

The major work for all operators will be the installation of the updated software that will change how the MCAS works. This controversial system has been the source of attention and debate throughout the MAX crisis.

The ‘new’ MCAS will rely on data from two AoA sensors, as opposed to one. If the data is erroneous and disagrees by 5.5o, the Speed Trim System, including the MCAS, will be disabled for the remainder of the flight. Both pilots will be warned of the disagreement by the AoA DISAGREE alert and the disablement of the STS. Additionally, the MCAS will only be able to fire off once per one event, as opposed to multiple times in the past. The limited magnitude of the nose-down movement will “preserve the pilot’s ability to control the aircraft’s pitch by using only the control column,” stated the FAA’s Airworthiness Directive. An extra layer of redundancy is added by the Flight Control Computers cross-monitoring each other, including the fact it will now detect rogue commands, including trim stabiliser commands.

The FAA has also demanded that operators change the horizontal stabiliser trim wire routing the installations to prevent a short-circuit in the wiring, which could cause a stabiliser trim runaway.

In total, the authority believes that installing the new software on the FCC, the revised MAX Display System and the stabiliser wiring modifications will cost up to US$10,760 per aircraft, including parts and labour.

So, will we likely now watch the rush, as airlines quickly pull their mechanics off furlough and set them to work on the vast stored fleets of MAX aircraft currently parked across the US?

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