The Boeing 737
The Boeing 737 was originally intended for short haul flights to short runways. One of the 737’s unique design features was that the engines were mounted on the underside of the wing, instead of in front of the wings on struts and pylons.
Mounting the engines hard up against the wing decreased drag, reduced weight, improved the aircraft’s center of gravity, made the cabin quieter, increased usable cabin space, and made the engines more accessible for maintenance. In addition, the under-wing engines just plain looked good.
Introduced in 1967, the Boeing 737 was an immediate hit. It eventually became the best-selling commercial aircraft in history.
The Type Rating
Before flying a jet, a pilot must have a license – or “type rating” – for that particular type of aircraft. That means a 747 pilot cannot fly a 737 without first obtaining a 737 type rating. Obtaining a type rating entails considerable training and FAA testing. Further, the pilot must renew his type rating regularly. That means more training and more testing. An airline that operates multiple aircraft types must therefore develop and maintain multiple training programs. Expensive.
Southwest Airlines decided it would save money by flying only one type of aircraft and one type only – the Boeing 737. All Southwest pilots hold and maintain the same rating – the 737 type rating.
Boeing 737 Variants
Over the years, Boeing has introduced a number of clean-sheet designs, such as the 787. It has discontinued older designs, such as the 757. But it has continued to develop and produce many variants of the 737. Versions are now available that hold up to twice the number of passengers as the original. The speed some versions of the 737 must fly when approaching the runway has increased dramatically, making it unsuitable for shorter runways at a small airports. Because many variants are so long, they carry a risk of striking the tail onto the runway during takeoffs and landings. Some versions of the 737 are not suitable for contaminated runways, as was the original. But the 737 remains extremely popular. One reason: all variants still qualify as 737s and thus can be flown on the same type rating.
Boeing 737 Max 8
As the aircraft became bigger, it needed different engines. The engines no longer fit under the wing. Thus, the Max 8 carries the engines in front of the wing instead of underneath. When the Max 8 pitches up too steeply, the engines can adversely affect that aircraft’s aerodynamics. To fix that problem, software activates the aircraft’s automatic trim system, commanding the aircraft to pitch down. If that safety system malfunctions and causes the aircraft to pitch down unnecessarily, the pilot can disable the system by switching off the automatic trim so that the trim can be controlled manually.
Lion Air Flight 610
Shortly after takeoff, the Lion Air 737 Max 8 pitched down unnecessarily in uncommanded fashion. The pilots attempted to physically overpower the automatic trim system instead of disabling it. The crash ensued.
Pilots are outraged that Boeing’s documentation does not explain to the pilot the operation of the automatic pitch down logic, called MCAS (for “maneuvering characteristics augmentation system”). Boeing says that exactly how the system works is irrelevant – the emergency procedure for an uncommanded pitch down is the same regardless of whether it was caused by the MCAS system or something else – simply disable the automatic trim system. Pilots respond that they are not mere checklist-followers. They need to know exactly how their aircraft systems work so they can understand why an aircraft is behaving in an anomalous fashion.
It now appears that Boeing did not specifically discuss the MCAS system in the pilot operating documentation because the more new material contained in the aircraft documentation, the more likely the FAA would require a new type rating — or at least more training — to fly it. Either of which would, of course, have defeated the whole purpose of modifying the 50 year-old 737 design yet again instead of designing the aircraft from a clean sheet of paper.
Ethiopian Airlines Flight ET302
The Ethiopian crash is in many was similar to the Lion Air Crash. Both aircraft were new 737 Max 8’s. Both crashes happened on the first flight of the day. Both happened shortly after takeoff, in good weather. Both aircraft had difficulty maintaining a stable climb before crashing. Could the Ethiopian crash also have been the result of the MCAS system commanding a nose-down pitch?
Boeing fans would say ‘no’. The real cause of the Lion Air crash, they say, was the pilots’ failure to disable the automatic trim system once the plane nosed over. Given the publicity surrounding the Lion Air crash, the Ethiopian Airlines crew would have been spring-loaded to turn off the system if they were experiencing the same problem. Therefore, the Ethiopian Airlines crash must have been caused by something else.