Page 30 - May 2019

Max Mania
by Kevin R. Dingman
Thrust Restoration system (ATR – the second, “hidden” system) uses the fuel controllers (causing no throttle movement) to add fuel when several unusual conditions are encountered simul- taneously during takeoff. And this system provides no system activation notification. With this system, as with the MCAS, any assertion that the manufacturer intentionally hid information from customers and pilots regarding their operation for some nefarious reason is unlikely. While the MCAS system is new to this aircraft, flight control augmentation, visible to the operator or not, is nothing new.
Innovation
Military and civilian aircraft designers have traditionally used imaginative, innovative and sometimes brilliant (Bell X-1, SR-71, SpaceShipOne) aerodynamic engineering in order to accomplish desired flight characteristics and capabilities. We have high-speed rudder limiters, flaps that “blow-up” when the limit speed is reached, a stick-pusher when AOA gets too high, slats that extend automatically at slow speed, even landing gear that extend on their own (Cherokee Arrow). We have anti-skid systems that override pilot aggressiveness, doors that won’t open inflight and multiple other systems that are “pilot-proof.” Almost all of the “below-the-surface” systems, however, alert the pilot when they are triggered.
When a new system is substantially similar to an existing system, or when failures in the new system display familiar failure modes or flight characteristics (and can be addressed with existing procedures), it’s not unusual for manufacturers to consider new designs, systems or components as relatively inconsequential to operating procedures and therefore, not pro- vide a pilot-alerting function in the system-activation logic nor recommend additional pilot training. Until that is, the brilliant new innovation displays an unexpected failure mode or proves to be overly complicated for Yogi or the other, average bears.
Why’d They Do It?
Boeing needed to make design changes to the venerable 737 in order to increase airline margins and thereby make the plane more competitive. To achieve this objective, a more efficient engine was chosen that was larger, but the engines needed more ground clearance. In order to avoid major airframe changes, the larger engines had to be moved higher, partially by making the nose strut longer, and partially by moving the engines forward. But the more-forward engines created unac- ceptable handling characteristics at high AOA. The Maneuvering Characteristics Augmentation System (MCAS) was designed to resolve the issue by adding to and changing the already existing Elevator Feel Shift (EFS) system (which makes the Max “feel” like a good-old-fashioned 737).
Most biz-jets and airliners like the Max have two AOA sensors but the “off the shelf, from the factory” MCAS only talks to one of
From the Flight Deck
Much has been written over the past several months about the reason(s) for the Boeing 737 Max crashes – and not just in aviation circles. The events garnered worldwide
attention not only because of their commonality, the perceived culpability of the manufacture and implied pilot training defi- ciencies, but because aviation crashes remain the modern-day version of a train-wreck. Passengers are at the mercy of the man, the machine, Mother Nature and the 10 million manufacturing and design decisions that were made years and decades before they ever boarded the plane. And we can expect this to be our aviation paradigm until civilian, multi-passenger space travel usurps aviation as the most sensational venue for transporta- tion disasters.
As you may imagine, those who pilot the 737 and its variants have been peppered with questions from inquiring minds that want to know. From family, friends, passengers, co-workers and other pilots we get questions such as, what do you think happened? Why didn’t they turn off the system? Would you feel safe flying the Max? The executive summary is this: Engineers created a “background” system using a marginally reliable, non- redundant probe/sensor; the crews didn’t recognize the failure mode; and yes, I would still fly the airplane. Here’s why.
Not the First Time
Systems and components that operate behind the scenes, oblivious to the crew are not new. The previous airliner that I flew, the MD-80, had two-engine related systems and one of them worked behind the curtain similar to the MCAS. They were the ART system and the ATR system – same letters but different systems to augment the motors during non-normal situations. We operators only discovered the existence of the Mad Dog’s second engine augmentation system through operational events that led us to query the manufacturer.
The Automatic Reserve Thrust system (ART) is an out-in- the-open, pilot-selectable/de-selectable system and uses the autothrottles to advance the remaining motor to a higher power setting after an engine failure. The system includes an an- nunciator that indicates activation to the crew. The Automatic
28 • TWIN & TURBINE / May 2019
PHOTO COURTESY OF BOEING