Sunday, March 17, 2019

Boeing: crashed and grounded

The crash of an Ethiopian Airlines plane, five months after the Lion Air crash in Indonesia, has forced Boeing to ground all its 737 MAX aircraft.

On October 29 last year, a two-month-old Boeing 737 MAX 8, operated by low-cost airline Lion Air of Indonesia, crashed approximately 12 minutes after being airborne, killing its 189 passengers and crew. The pilot, with more than 6,000 flight hours and the co-pilot, with more than 5,000 hours, formed an experienced team. Last Sunday, on March 10, another flight by a four-month-old 737 MAX 8, operated by Ethiopian Airlines, crashed approximately six minutes after takeoff. All 157 passengers and crew were killed.

The disparity in the flight hours of the crew, about 8,000 for the pilot, and just 200 hours for the co-pilot, has led to some scrutiny. Similarities between the two events, of the flight crew reporting certain technical difficulties, requesting a return to base, the scientific tracking of an unstable flight trajectory and airspeeds and also the ‘gathering of some technical evidence’ (in Ethiopia), have led analysts to conclude that there could be an issue with one of the aircraft’s key control systems. It may take time for data from the black boxes to be analysed and acted upon.

How did India react?
It was in two quick stages, which impacted the operations of the country’s two 737 MAX operators, private airlines Jet Airways and SpiceJet, with a fleet of 5 and 12 aircraft respectively (according to data from the Directorate-General of Civil Aviation, the country’s nodal aviation agency). Another aircraft data site puts the fleet composition at 9 and 14 respectively. The DGCA initially permitted operations to continue, with key directives that kicked in from March 12.

In a notice, dated March 11 (now withdrawn), taking into account “compliance of all manufacturer Standard Operating Procedures/operations circulars and Federal Aviation Administration [FAA] emergency Airworthiness Directives,” it advised additional actions for airline engineers and maintenance crew such as “no minimum equipment list (MEL) release” — a list which allows aircraft operation, under specified conditions — if there were control system red flags. It also mandated key checks during aircraft transit. Finally, flight operations departments were to ensure, among other things, that the minimum experience levels of the two pilots were “1,000 and 500 hours” respectively.

The DGCA said these were “interim safety measures” and there was communication with the manufacturer and the FAA. On March 13, it issued a follow-up notice, deciding that “the operation of B-737 MAX aircraft would not take place from/to Indian airports and transit or enter into Indian airspace effective from March 13 till further notice.” All operations ceased by 4 p.m. local time.

How was it overseas?
The ban was rolled out in phases. In the Asia-Pacific region, the grounding, on March 11, by the Civil Aviation Administration of China, which took the global lead, has hit the largest 737 MAX fleet in operation. Figures (compiled in early March 2018) from a leading fleet data site show that of the estimated 371 MAX aircraft in operation, a quarter, or close to 97 planes, are used by a raft of China-based airlines. With over 50 operators based in 34 countries, the Asia-Pacific region is the base for close to 37% of the worldwide fleet. The U.S. follows next with 30.2%. The situation was a bit different in the U.S., with the FAA playing outlier and then announcing a grounding.

Is the aircraft flawed?
We don’t now as yet. Some media reports cite the huge financial impact of the global grounding per day and potential damage to an order book estimated to be several billions — there is even a figure of “half-a-trillion dollars” floating around.
But the main attention is now on a control system in the plane. Preliminary analysis of both crashes has focussed on the “anti-stalling system” called the Manoeuvering Characteristics Augmentation System (MCAS). It was introduced after the newer and more fuel efficient engines for this aircraft type, which have a much larger diameter and heavier weight than earlier ones, have had to be fixed higher and more forward on the wings than done previously for the earlier 737 models, consequently making changes to the aircraft’s flight profile. As a result, there has been a possibility of the aircraft, while in flight, pitching a bit more higher than intended. In certain stages of flight, this could lead to what is called a stall which can have dangerous consequences.

The automated MCAS comes in here. With the Angle of Attack (AoA) sensors, it detects when the aircraft is at risk and initiates corrective manoeuvres using the stabilisers. A senior Boeing 737 pilot told The Hindu that the MCAS is supposed “to work quietly in the background.” The MCAS could force the aircraft into a dive if there are erroneous inputs from the AoA sensors (An FAA emergency airworthiness directive highlighted this). After the Indonesia crash, some pilot unions, especially in the U.S., flagged it as being a nasty surprise and there having been inadequate exposure to, information about and training for this feature. There is some commentary on this putting it down to the manufacturer not thinking of creating awareness of this feature to be a necessity.
16/03/19 Murali N. Krishnaswamy/The Hindu