Flying blind
Just over two weeks ago, an almost new Boeing 737 MAX8 dived into the Java Sea in Indonesia with the loss of all lives on board. The crash attracted a great deal of attention because it involved the first example of the newest variant of the 737 to be lost, and because the airline involved has attracted some criticism of its safety record in the past. As the investigation got underway, issues emerged that pitched manufacturer, pilots and unions into vigorous debate and has already resulted in a safety notification being issued to operators of the jet. Although the final report on the accident is still a long way in the future, The Aviation Oracle looks at some of the issues involved.
Imagine you’re driving a shiny new car on cruise control. It’s quite a sophisticated vehicle and when it detects you’re getting too close to an object in front, it brakes for you. Great. However, the manufacturer configured the system so that once the road ahead clears it accelerates back to the speed that was set previously. That might be OK on many occasions, but perhaps not always. Oh, and the manufacturer hasn’t told you the car will do this. Even so you might still be fairly happy with the concept. But consider what it would be like if you can’t see through the windows – the only thing you have to go on is the speedo, and for the most part you have to ‘trust’ what the car is doing. Still comfortable?
As near as can be explained in layman’s terms, something similar has happened with the 737 MAX, the latest version of Boeing’s best-selling short-haul airliner. This new variant’s large low-slung engines are installed further forward and are canted up slightly to avoid them scraping the ground. But doing that increased – albeit only slightly – the risk that the aircraft might stall. This is not the same as a stall you occasionally get in a car – it happens when an aircraft is flown too slowly, or its nose is pitched up too much. A stalled wing doesn’t produce sufficient lift to keep an aircraft in the air, so it drops. And if the pilots don’t implement an expedient recovery the result could be a crash. Naturally pilots are trained to recognise conditions and instrument readings that could indicate the onset of a stall, and deal with it safely. However, since on-board software has become ever more sophisticated, manufacturers have implemented automated systems that help prevent a stall. These move the controls even if the pilots don’t react in an attempt to avert disaster, and for the most part they are an excellent safety measure. This is essentially what Boeing did with the 737 MAX – it installed what it called a Manoeuvring Characteristics Augmentation System (MCAS) designed to avert a stall by applying nose down trim, but it didn’t tell pilots what it had done. MCAS wasn’t a feature of earlier 737 variants, nor was it covered in the ‘differences’ training all pilots receive when they transfer onto an aircraft they haven’t flown before.
Lion Air 610
On October 29, Lion Air flight JT610 departed from Jakarta, Indonesia bound for Pangkal Pinang with 189 people on board. Thirteen minutes later is crashed into the Java Sea. Boeing 737 MAX8 PK-LQP was two months old and had flown a mere 800 hours since delivery; it was an almost new aircraft. During its short final trip aloft the pilots requested clearance to return to Jakarta, but the aircraft hit the Java Sea in a steep nose-down attitude 21 miles from the airport.
Fluctuating height and abnormal speed readings were transmitted to the ground by the aircraft’s systems. As an investigation got underway, the National Transportation Safety Committee revealed that there had been problems with the aircraft’s angle of attack (AoA) sensors and airspeed indicator on its last four flights. Replacement of some components had taken place, which had been expected to remedy the faults.
Theories
It is suspected that sensors – probes on the outside of the aircraft – might have been sending erroneous data to the on-board computers. If that was the case, the aircraft’s computers could have “thought” the aircraft was flying slower – or its nose was pitched up more steeply – than was actually the case. And when the computers detected the risk of a stall, they forced the nose of the aircraft down by applying nose down trim to the control surfaces on the horizontal tail. The pilots could counter the intervention of the computer and get things level again, but after ten seconds the process would start again. The Lion Air pilots didn’t know about the new system so it’s possible they could have been confused: the aircraft was going fast enough, the nose wasn’t pitched up steeply, and yet the controls were being forced downwards. Whatever happened on board, the end result was tragic.
Airworthiness authorities have since issued advisories to airline customers and pilots, making them aware of the MCAS and how to switch it off. It’s possible that there could be minor changes to the 737 MAX design in future, particularly if it is proven that faulty sensors were the root cause of the crash. But the fundamental question for now is – should pilots be made aware of systems and their effects when they are trained to fly a new aircraft type?
Staying in the loop
Learning to fly an airliner isn’t like learning to fly a car. Every commercial pilot receives very thorough training, not only in the art of flying but also on the systems in the aircraft they are going to fly. They are taken through faults that could arise, problem diagnosis, and resolution actions. Take for example a strong burning smell and smoke. In a car, you might stop and get out and find out what’s wrong. In an aircraft at 35,000ft it’s not that easy. But pilots are trained to know where the air they are breathing comes from – which engine provides the supply to the cockpit for example – and can thus take informed action to eliminate the problem before it becomes fatal, even if that means deactivating a system or shutting down an engine.
A lawsuit alleging a fault in the 737 MAX design has already been filed. It claims that “under certain conditions [the MCAS] can push the nose down unexpectedly and so strongly that the pilot cannot pull it back in time to avoid a crash.” It adds: “It is particularly surprising to hear from safety experts… that Boeing failed to warn its customers and the pilots of its new 737 MAX aircraft about this significant change in the flight control systems.”
The Aviation Oracle doesn't wish to pre-empt the findings of the ongoing investigation. It may be that the probes and the software were fine, and the tragic accident was a result of another cause. But a pilot training omission has already been acknowledged. Providing pilots with an intimate understanding of the workings of machines they fly is vital. Failure to do so could have ramifications for the safety of every airline passenger unfortunate to be in the wrong place at the wrong time. Let’s not make the same mistake again.