If a visitor listened only to the first hour of the June 24 NTSB hearing into the Asiana Airlines 777 accident at San Francisco International Airport (SFO) on July 6 last year, no one could fault him for assuming the pilots bore the lion’s share of responsibility for the crash. That’s all the Board spoke of, at least initially. The two Asiana pilots were, after all, two high-time captains in command as the Boeing 777 slipped lower and lower on a PAPI-generated glideslope during a visual approach in severe-clear weather. The Boeing also slowed to as much as 30 knots below the targeted final approach speed with no corrective action from either pilot. When the pilots did finally attempt a go-around about four seconds before impact, their efforts were too little too late. The 777 ripped open after the main gear and aft fuselage struck a seawall near the approach end of SFO’s Runway 28 left. Three people died in the accident, two of them passengers ejected from the aircraft at impact that the NTSB believes were not wearing seatbelts. One hundred eighty-nine of the 304 others aboard were injured, 49 of them seriously.
The remainder of the hearing examined a number of contributing factors such as confusing manufacturer documentation about the intricacies of the 777’s autothrottle system and the fact that some Asiana instructors didn’t understand the autothrottle system all that well themselves. In all, NTSB investigator-in-charge Bill English identified 14 separate safety items (see box) and the NTSB proposed 27 different recommendations in these areas to the FAA, Boeing, Asiana Airlines, the City of San Francisco and Aircraft Rescue and Firefighting Working Group.
Specifically, the NTSB determined the probable cause of the accident to be the flight crew’s mismanagement of the airplane’s descent during the visual approach; the pilot flying’s unintended deactivation of automatic airspeed control; the flight crew’s inadequate monitoring of airspeed; and the flight crew’s delayed execution of a go-around. Contributing to the accident were the complexities of the autothrottle and autopilot flight director systems, which the NTSB said were inadequately described in Boeing’s documentation and in Asiana’s pilot training, raising the likelihood of mode error. The Board also cited the flight crew’s nonstandard communication and coordination regarding the use of the autothrottle and autopilot flight director systems; the pilot flying’s inadequate training on the planning and executing of visual approaches; the pilot monitoring/instructor pilot’s inadequate supervision of the pilot flying; and flight crew fatigue after the long trip from Seoul, which likely degraded their performance.
In a question-and-answer session after the technical presentations, Board member Robert Sumwalt challenged some of the doubts raised publicly about the competence of the Asiana crew. “I don’t happen to believe this accident is about crew competency,” he said. “Yes, the instructor pilot could have been better trained to oversee his trainee, but the pilot flying had more than 10,000 hours. I think this is a case of the pilot flying expecting the aircraft to do something…it was not designed to do. That expectation came from training that may have misled him, but also from documentation that our investigation showed was not totally clear. The ground instructor who taught the pilot monitoring [on this flight] described the autothrottle going into the hold mode as an anomaly. It’s not an anomaly. It’s the way the aircraft was designed to operate.”
Sumwalt also stated that one Asiana instructor knew of at least three instances in which other pilots had been confused by the 777’s autothrottle logic yet took no apparent action to change the company’s training procedures. Sumwalt said other Boeing 777 operators told him the aircraft’s autothrottle hold mode was not well understood [in the field]. Senior air safety investigator Roger Cox countered by explaining that the autothrottle logic used on the 777 was the same that has been in use on all Boeing widebodies since the introduction of the 767 in the early 1980s.
The pilot flying Asiana 214 on July 6 was already an A320 captain transitioning into the 777 and had logged 33 hours in type; the pilot monitoring was newly certified as a 777 instructor with 3,200 hours in type.
Final Minutes of Asiana Flight 214
The NTSB’s English took the Board through the final minutes of the flight. The pilot flying initially set 1,500-fpm descent in the autopilot because the aircraft was high, an action that did bring the airplane back to the glidepath. At a six-mile final, the descent rate was reduced to 1,000 fpm and 3,000 feet was set in the master control panel (MCP) in case of a go-around. The aircraft passed the final approach fix still 400 feet high and the crew continued to reduce airspeed.
The pilot flying called for flaps 30. The pilot monitoring countered, explaining they were above safe flap speed. The pilot flying then switched the autopilot to flight-level change (FLCH) mode, which had no effect on the rate of descent and is not a selection recommended for use on final approach. The pilot monitoring most likely missed the mode change because he was waiting for the aircraft to decelerate to the flaps-30 speed. The flying pilot’s mode change to FLCH actually commanded the 777 to climb to the 3,000 feet previously set.
The pilot flying then called for flight director off, which was part of Asiana’s SOPs for visual approaches. Asiana procedures require both flight directors to be turned off simultaneously before the pilot monitoring could be allowed to turn his back on to monitor the final approach. The simultaneous switching off of both flight directors would have reset the autothrottles and cleared previous functions–such as the impending autothrottle hold–allowing them to control airspeed again. However, the two flight directors were never turned off at the same time. The NTSB learned that flight director cycling was only an informal Asiana procedure and one that Boeing manuals and training procedures did not explain as an option for clearing an autothrottle setting.
To prevent the Boeing from climbing, the pilot flying switched off the autopilot and pulled the throttles to idle, which placed the Boeing’s autothrottles into the hold mode and no longer controlling airspeed. At the 500-foot point on final approach, sink rate increased to more than 1,000 feet per minute. The pilot monitoring did not make the required 500-foot callout on this approach. As the descent rate increased to 1,500 feet per minute, the instructor said only, “sink rate.” At about a mile-and-a-half from the end of the runway, the aircraft passed through the visual glideslope and slowed below the target approach speed. The pitch attitude steadily increased as the pilot flying pulled back on the wheel to maintain the glidepath, which the aircraft continued dropping well below. The airspeed was now 15 knots below Vref and continuing to decay.
As the control column reached the full-aft position approximately 11 seconds before impact, a low-speed alert was heard in the cockpit. Seven seconds before impact, the instructor in the right seat advanced the throttles just as the stick shaker activated. It was only now that the pilot monitoring called for a go-around. The 777 could not comply and the main gear and the aft underside of the fuselage struck the seawall.
The NTSB presentation revealed that the visual approach that ended in disaster at SFO that day was the first the pilot flying had flown without an electronic glideslope outside the simulator. He said he did not feel confident and did feel stressed. It was only after this accident that Asiana added straight-in visual approaches to its training syllabus. The pilot flying needed active coaching and showed poor awareness of altitude and airspeed, but at no time did the pilot monitoring intervene. Asiana did not encourage manual flying by its pilots and often allowed them to hand fly only once the aircraft was already stabilized on final approach. The pilot flying never trimmed the airplane after turning off the autopilot.
Dr. William Bramble addressed the flight’s human-performance issues. “The flight crew mismanaged the aircraft’s vertical approach, which resulted in the aircraft being too high, delay[ing] deceleration, increas[ing] workload and increas[ing] the possibility of errors. It also degraded monitoring and reduced the option to catch [and correct] errors. These likely played a role in the flying pilot’s choice of FLCH and the other pilot’s missing that change. Due to the complexity of the autothrottles system logic and inadequacies of the 777 documentation, the pilot flying had an inaccurate understanding of the 777 flight logic system…and believed the autothrottles would provide low-speed protection when they would not.”
Board member Mark Rosekind asked senior accident investigator Roger Cox to detail the number of actions or inactions that occurred during the approach to SFO. Cox said that from 14 miles out, he counted roughly 20 to 30 compounding errors. For instance, despite excess aircraft energy, the flying pilot never used the speed brakes. Also, even with three pilots in the cockpit (one reserve pilot), no one noticed how long the throttles remained pulled back to idle. The Board believed the crew was likely experiencing fatigue, because at 200 feet, despite an unacceptably low glideslope indication as well as low airspeed, neither pilot took action for 11 seconds.
“In this investigation we have learned that pilots must understand and command their automation and not become reliant on it. The pilot must always be the boss,” said Board member Christopher Hart in concluding the meeting. Findings, recommendations and animations presented at the hearing are available at ntsb.gov.
Safety Issues Raised by the Crash
• flight path management
• adherence to standard operating procedures
•flight crew monitoring procedures
• flight instructor operating experience proficiency
•manual flight proficiency
•understanding of the autothrottle logic system
•777 autoflight system airspeed control
•appropriate use of flight directors
•low-energy alerting systems
•injury potential from lateral forces
•slide-raft certification standards
• ARFF training and staffing
•SFO emergency procedures
