Technology, Pilot Beware
By Captain Chuck Valle
"Technology has positively improved aviation safety in countless ways. As with every solution, a seed is also planted for the next problem. Advancements in avionics technology now enables an airplane to be flown using a coupled autopilot in parts of the flight envelope regime not allowed to be hand flown. But when technology malfunctions in this regime, the pilot is still expected to hand fly the airplane to safety. That’s a problem!
In February 1998 a Boeing 727 suffered a “classic ‘systems accident’ caused by a known equipment deficiency” according to NASA scientist Dr. Key Dismukes in his book The Limits of Expertise: Rethinking Pilot Error and the Causes of Airline Accidents. The Boeing 727 crashed 314’ short of the threshold of runway 14R at O’Hare International Airport while on a CAT II approach in 1,400’ RVR weather. “The autopilot-induced oscillations caused the airplane to enter a steep descent when it was very close to the ground. The NTSB determined that the probable cause of the accident was ‘the failure of the flight crew to maintain a proper pitch for a successful landing and go-around’.”
This accident was categorized as controlled flight into terrain. A well-known category which often puts blame on pilots and may not be suited to analyze an aircraft accident when a technology malfunction is controlling the aircraft flight path. Dr. Dismukes states, “It is detrimental to the cause of aviation safety to assume that the failure stems from deficiency of the crews.”
Sometimes there are existing concerns that might reduce the margin of safety and pilot judgement calls for a change in the plan. Too many accidents occur because crews “…continue with an existing plan.” Using technology that puts the flight crew in a scenario requiring split second decision making is inherently risky. With an aircraft on autopilot, just when and how quickly pilots react to deficiencies in the flight path can make the difference between a safe flight or an accident.
Humans respond to expected stimulus much more quickly than unexpected stimulus. Standard Operating Procedures (SOP’s) help avoid the ‘Startle Factor’. In this classic systems accident using Category II procedures, the first officer flew the approach and at 135’ AGL the Captain took control of the airplane with the “I’ve got it” call as the approach lights came into view, initially leaving the autopilot coupled. Two seconds after taking control the flight recorder showed the airplane on glideslope with a changing nose low attitude revealed to the crew as they acquired more outside visual references.
Dr. Dismukes said, “Alerted to the danger, the Captain’s response to correct the situation (adding power and pulling back on the yoke) occurred one second later.” “The Captain’s response was rapid compared to the expected human response time to react to an unexpected event.”
“However, in its report on this accident, the NTSB did not provide a rationale for whether and how crews might be expected to reliably react in time to correct a critical moment” induced by a technology malfunction in control of the flight path.
That’s a problem.
THANK YOU Chuck!
Enjoy the Journey!