Safety The Human-Engine Interface Many problems, one easy solution BY JAMES ALBRIGHT [email protected] y first piece of aircraft auto- you to engage the autothrottles for autothrottles had a role to play leading SAICLE/GETTY IMAGES mation was a flight director in takeoff and then simply forget about up to the scene of the accident. Four fol- the Northrop T-38. It was pure them until after landing. And, I must low — each with an autothrottle prob- magic: Two mechanical needles admit, sometimes I forget about them. lem. Let’s see if we can come up with a Mcame into view, one for course and an- But these days, I mostly don’t trust solution. other for glidepath, and you simply flew them during the climb because with the airplane so as to center them. Over the wrong mode of the autopilot they Case Study: Gulfstream the next few years the crossbars turned can result in a stall. Oh yes, I don’t trust GIV, G-GMAC to vee bars, but there was nothing them en route because changing envi- earthshaking until one of my airplanes ronmental conditions can leave us short Problem: There has been a divergence of allowed us to couple those bars to the of thrust. And then there is the descent. opinion in the Gulfstream world on the autopilot. Now, that was neat. And don’t get me started about the ap- proper way to engage and disengage Then came an autothrottle system proach phase! OK, OK. I guess I just the autothrottles. There are two sets of that was good for an ILS approach and don’t trust them. But I do use them from switches, forward and aft of what are autoland, but not much else. (It could not takeoff to landing; they free up my brain called throttles, power levers or thrust be trusted for takeoff or climb.) for other things. levers. The type of switches used has It wasn’t until I got to the Gulfstream Why so paranoid? There have been a changed but their locations remain the GV that I had an airplane that allowed lot of accidents over the years in which same. The forward switches will only disengage and the aft switches will en- gage or disengage. You can only engage with the switches aft of the throttle stems, so no debate there. I believe you U.S. AIR FORCE should only disengage using the forward switches, since there is no chance you will engage the autothrottles with a “double click.” But Gulfstream gives us the option and it seems many pilots use the aft switches for everything. On Dec. 1, 2004, a crew destroyed a perfectly good airplane while land- ing at Teterboro Airport (KTEB), New Jersey. The pilot disengaged the auto- throttles at 570 ft. AGL. It is unclear as to who or why, but the autothrottles were re-engaged at 38 ft. The GIV can- not be landed with the autothrottles en- gaged and I speculate that the pilot hit Northrop T-38 attitude director indicator, circa 1979 the aft engage/disengage switches at 56 Business & Commercial Aviation | August 2020 AviationWeek.com/BCA Case Study: Turkish Well, maybe they were. Here’s my Airlines Flight 1951 take: The radio altimeter system was one of the leading maintenance squawks KEVIN KNECHT Problem: Does this sound topi- for the Boeing 737-800 of the time — in cal? A Boeing 737 equipped fact, it was the top squawk at Turkish with two sensors used by the Airlines. Boeing knew a faulty radio al- automated flight system was timeter could cause an autothrottle “re- designed to use only one of tard” mode while in flight but reasoned those sensors at a time, ignor- that the cockpit had more than enough ing the opposite sensor. Then warning systems to alert the crew. one day the sensor being used Actually, the very airplane involved in went bad and the airplane this crash had the “retard” mode occur crashed, even though the op- in two previous flights in the previous posite sensor could have saved 48 hr. But each crew noticed the “RE- the day. It has nothing to do TARD” annunciation, the decaying air- Gulfstream GIV autothrottle switches with the 737 MAX of the Lion speed, the low-speed cue and the higher the last moment to ensure they were Air Flight 610 era; this was 10 years ago. than usual deck angle. Each crew dis- disengaged. Of course, that caused them In a nutshell, here is what happened connected the autothrottles and flew the to re-engage. to Turkish Airlines Flight 1951 on Feb. jet to a successful landing. This crew After landing when the speed de- 25, 2009: The captain’s radio altimeter did not. Rather, the captain was busy cayed below the target approach speed, malfunctioned to read -8 ft. in flight. training a new first officer, but there the autothrottles pushed the thrust le- DUTCH SAFETY BOARD vers forward, making it impossible for the pilot to lift the reverse levers out of their stowed detent. With available runway disappearing, the pilot activated the emergency brake, which does not have anti-skid protec- tion, and the airplane departed the run- way. All survived the landing except the airplane. The NTSB blames the crew’s inad- vertent engagement of the autothrot- tles and failure to recognize that during landing. The Safety Board also notes the lack of autothrottle switch guards and a lack of an audible engagement tone. But Turkish Airlines Flight 1951 flight mode all of that misses the point. annunciations during approach Once the airplane had been landed the pilot should have noticed the throt- tles moving forward and he should have The crew were slam-dunked into Schi- was a third pilot on the flight deck as slapped them back. I am speculating phol Airport, a common occurrence. A a safety pilot. Nevertheless, they got that the pilot’s right hand was not on the poor design allowed the autothrottles rushed with the slam dunk and nobody throttles during the final phase of the to use the left radio altimeter while the noticed the visual cues and five audible approach and landing until he wanted first officer flew the ILS with the autopi- warnings until the stick shaker alerted the reversers. lot coupled to the right autopilot. As the them, too late. Solution: Keep your hands on the aircraft intercepted the ILS from above, Solution: Keep your hands on the the autothrottles had all they needed throttles during approach and landing, NTSB to go into “retard” mode. Neither pilot DUTCH SAFETY BOARD seemed to correlate a cascading series of warnings, including one for low air- speed, and the resulting high deck angle, with the radio altimeter failure. The 737 ran itself out of speed at about 500 ft., at which time it stalled. The airplane impacted short of the run- way. Nine of the 135 people on board were killed. The airplane was destroyed. Gulfstream GIV G-GMAC The Dutch accident investigators Turkish Airlines Flight 1951 wreckage throttles during approach and landing, placed the blame on Boeing for the de- and mentally connect what they are do- sign of the radio altimeter/autothrottle and mentally connect what they are do- ing against what you want them to do. If interface while giving the crew an addi- ing against what you want them to do. If there is a disagreement, put the throt- tional mention, as if they were bystand- there is a disagreement, put the throt- tles where you want them. ers to the crash. tles where you want them. AviationWeek.com/BCA Business & Commercial Aviation | August 2020 57 Safety Case Study: Asiana mode control panel or flight manage- will be surrounded by a green box for Airlines Flight 214 ment computer. 10 sec. The A/T will remain in HOLD υ࠙Thrust (THR) — Thrust applied to mode until one of the following condi- Problem: Airlines in South Korea have maintain the climb/descent rate re- tions is met: a long history of crashing airplanes be- quired by AFDS (autopilot flight direc- (1) The airplane reaches the MCP tar- cause their pilots had difficulty when tor system) pitch mode. get altitude. they were deprived of an ILS signal and υ࠙Idle (IDLE) — Occurs when A/T (au- (2) The pilot engages a new AFDS their crews were unwilling to challenge tothrottle) controls the thrust levers to pitch mode or new A/T mode. the most senior pilot on the flight deck. the aft stop. (3) The A/T arm switches are turned This particular crash fits that mold, but υ࠙Hold (HOLD) — Occurs when A/T re- off. the design of the autothrottle system moves power from the servo motors. In (4) The thrust is manually com- combined with poor pilot technique was this mode, A/T will not move the thrust manded to increase past the thrust certainly a factor. levers. limit. On July 6, 2013, Asiana Flight 214, υ࠙Flight level change (FLCH) — A mode (5) The A/P is disconnected, and both a Boeing 777, was on approach to on many autopilots that holds speed by F/D switches are turned off. San Francisco International Airport either bringing the throttles to idle or This seems nonsensical at first. If (KSFO) on a clear day with no real chal- climb thrust while controlling speed you are in an idle descent why do you lenges to speak of, except maybe one. with the elevator. want the autothrottles to essentially The ILS glideslope was out of service. I am familiar with all of these modes stop moving once they hit idle? To ra- While many U.S.