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13 July 2013

Summary of final two NTSB briefings on Asiana 777 plane crash in San Francisco

On Wednesday, 10 July 2013 and Thursday, 11 July 2013, NTSB conducted their final two press conferences in San Francisco, and covered a variety of issues around the accident, including the operation of the autopilot and autothrottle, damage to the airplane, injuries to the flight attendants, the evacuation of the aircraft, and other initial factual findings from the investigation.

The NTSB emphasized in both of these press conferences that the information was factual in nature, and in many cases had not yet been confirmed or corroborated. For example, statements received from the flight crew still have to be matched up with information from sources such as the cockpit voice recorder (CVR) and the flight data recorder (FDR).

Cockpit automation and its role in the crash
As mentioned in a previous article, use of the autothrottle by the crew to maintain speed was an issue because although the crew was heard on the CVR stating that the target speed was 137 knots, the aircraft was significantly slower than that speed before the crash. In Wednesday's press conference, the NTSB stated that there were five distinct autothrottle modes used in flight, and in the last 2.5 minutes of flight, there were several autothrottle and autopilot modes used.

As explained by the NTSB, the autopilot helps pilots manage pitch, roll, attitude, and heading; while the autothrottle helps to control speed or thrust. The two systems can work together, and the NTSB has to determine, with the help of Boeing, the following:

  • Whether autopilot and autothrottle modes were commanded by the pilots or activated inadvertently,
  • How the various autopilot and autothrottle modes are designed to work, and
  • What are the ways the systems are expected to respond in the various modes.

Comparison to automobile cruise control
NTSB chair Deborah Hersman used an analogy to a much simpler automated system to illustrate the role that an autothrottle plays. Like in an airliner, a car's cruise control can be set to a specific speed, but it is up to the driver to monitor the speed. Also, cruise control may not engage if the car is in a particular mode, for example below a certain speed. While in cruise control, the driver may be allowed to increase or decrease speed within certain limits. Disengaging cruise control can be done by disarming the system or by hitting the car's brake.

Status of the pilots on flight 214
There were a total of four pilots on board, and they consisted of two crews. The first crew consisted of a training captain going through his initial operating experience (IOE) on the 777 and an instructor pilot (IP) who was a training captain. The relief crew consisted of a captain and a first officer (FO) This first crew performed the takeoff from Seoul and flew for several hours before the relief crew took over, and then the first crew flew approximately the last 1.5 hours of the flight.

Shortly before landing, when the aircraft was at around 10,000 feet, the relief FO entered the cockpit and was in the jumpseat for the rest of the flight. The NTSB provided details on the experience of the three pilots in the cockpit:

  • The training captain was in the left seat at was the pilot flying (PF),
  • The training captain had about 9,700 total hours, including about 5,000 as pilot in command (PIC),
  • The PF was hired by Asiana in 1994, and trained in Florida,
  • The PF was rated to fly the 737, A320, 747, and 777, and from 2005-2013 flew the A320, serving as an A320 captain before moving to the 777,
  • The PF was also a ground school and simulator instructor for the A320 and A321
  • The IP was also a 777 captain who served in the South Korean air force for about 10 years before joining Asiana,
  • The PF's IOE was to consist of 60 flight hours and 20 flight legs, and had gone through 10 flight legs and about 35 flight hours at the time of the crash,
  • The IP had about 13,000 flight hours, including about 3,000 in the 777, and 10,000 as a PIC,
  • The IP served as the PIC on flight 214, and was sitting in the right seat,
  • This flight was the first time that the PF and the PIC had flown together, and it was the PIC's first trip as an instructor pilot
  • The relief FO was a former F-5 and F-16 pilot in the South Korean air force, and had about 4,600 total hours, including 900-1,000 hours in the 777,
  • The relief FO had flown to San Francisco five or six times as an observer.

Landing aids in use at the airport
Air traffic control was allowing pilots to operate under visual flight rules (VFR) when flight 214 was approaching the San Francisco airport (SFO), which means that pilots were not required to use the instrument landing systems at the landing runway (28L) or any automated systems on their aircraft. One of the electronic aids that provide aircraft guidance on their glide slope was inoperable, but this had been published for some time and all flight crews using the airport should have been able to see this information. The NTSB has not stated if this crew were aware of this.

A glide slope aid that was in operation at runway 28L were the precision approach path indicator (PAPI) lights, a set of four lights arranged in a horizontal line that provide pilots with a visual indicator of whether the aircraft on the glide slope, above the glide slope, or below the glide slope.

A pilot who is on the glide slope would see two sets of red lights on the left and two sets of white lights on the right. In the example shown here (not from SFO), the three left indicators are red and the right one is white, indicating that the aircraft is slightly below the glide slope. Four red lights would indicate that the aircraft is well beloe the glides slope, and four white lights is an indicator of being well above the glide slope.

Final approach sequence
Over the last two press conferences, the NTSB discussed the following key parts of the final approach:

  • The approach path took the aircraft directly over SFO, followed by a wide teardrop left turn to line up with the runway (see below),

    (click to enlarge)
  • Air traffic control (ATC) called for a maximum airspeed of 180 knots until the aircraft was five miles out,
  • The IP recalled that the aircraft was above the intended glide path at 4,000 feet, and that vertical speed mode was set at 1,500 feet per minute,
  • ATC gave a landing clearance about 1.5 miles from the runway, about 90 seconds prior to the crash,
  • There was a sink rate callout prior to the aircraft reaching 500 feet,
  • At about 500 feet, the FP noted a blinding flash of light directly in front of the aircraft but not on the runway,
  • The FP stated that he looked away into the cockpit, and was able see the cockpit instruments, including the speed tape,
  • There was no mention of the light on the CVR,
  • The FP believes it may have been a sun reflection, and the NTSB is determining if this could have been the case,
  • There was an automated 500 foot callout about 35 seconds before the crash,
  • Shortly after this callout, the landing checklist was completed,
  • At about 34 seconds prior to impact, the IP noted that the aircraft was below the glide path at 500 feet, and speed was at about 134 knots, with three red PAPI lights showing, and told the PF to pull back
  • Autothrottle was armed and set at 137 knots
  • between 500-200 feet, the IP noted that there was a lateral deviation and that the aircraft was low,
  • At 200 feet, the IP noted four red PAPI lights, that the speed tape was hatched (a visual indicator of an impending stall), and that the autothrottle had not maintained speed,
  • There was an automated 200 foot callout 18 seconds before impact,
  • There was an automated 100 foot callout nine seconds before impact,
  • Almost immediately after this 100 foot callout, a crew member mentioned airspeed (the NTSB noted that there were no mentions of speed heard on the CVR between 500-100 feet),
  • About three seconds before impact, there was a call for a go around,
  • The IP established a go around attitude, and went to push the throttles forward manually, but saw that the FP had already done so,
  • A second call made for a go around was made by a different crew member about 1.5 seconds before impact.

Crash sequence

  • The main landing gear hit the sea wall first, followed by the tail section,
  • The main landing gear sheared away from the aircraft as designed, and the wing fuel tanks were not punctured by the gear separation or during the the rest of the crash sequence,
  • Cabin flooring and galley components were found on the chevrons in the runway overrun area between the sea wall and the runway threshold,
  • The initial impact displaced rocks from the sea wall and some of them were distributed several hundred feet along the debris trail (see photo below),

    (click to enlarge)
  • All passenger seats stayed inside the cabin, but three flight attendant seats were ejected onto the runway,
  • Door 4L detached from the aircraft at some point in the crash sequence
  • Six of the 12 flight attendants were interviewed, and they stated that two of the eight escape slides inflated inside the cabin after a secondary impact (from a witness video, it appears that the aircraft rotated almost 360 degrees counter clockwise, with the rear of the cabin rising up at an angle before hitting the ground at the end of the crash sequence),
  • The right engine had detached from the wing, had rotated about 90 degrees counter clockwise, and was laying alongside the fuselage (see photo below).

(click to enlarge)

Post-crash actions and fire

  • After the aircraft came to a stop, the lead flight attendant (who was near door 1L) went to the cockpit for advice, and was advised not to initiate evacuation (see door layout in photo below),

    (click to enlarge)
  • Fire extinguisher switches were pulled for both engines and the auxiliary power unit,
  • The flight crew was able to communicate with the control tower, and the cabin crew was able to use the public address system to communicate to passengers,
  • A flight attendant who was trained as a lead flight attendant was at door 2L, saw fire outside door 2R near row 10 of the aircraft, and sent the other flight attendant at door 2L to the front of the cabin to inform the rest of the crew about the fire and the need to evacuate (in earlier briefings, the NTSB stated that the source of the fire was a ruptured oil tank that leaked fuel onto hot engine parts from the right engine),
  • Passenger evacuation began about 90 seconds after the aircraft came to a stop, escape slides were first deployed from door 2L and then from door 1L, and passengers also escaped from door 3R,
  • The control tower called for emergency vehicles after the aircraft hit the runway, the first vehicle arrived about two minutes after the crash, and extinguishing agent was first applied about three minutes after the crash,
  • Cabin emergency exit lighting came on during the evacuation,
  • There were six flight attendants who were injured and hospitalized: three seated in the rear of the plane who were ejected out onto the runway, another flight attendant in the rear who was injured, and two who were injured by the slides that deployed inside the cabin including one at door 1R and a second at door 2R,
  • The remaining six flight attendants had evacuated most of the passengers by the time the fire had spread to the cabin,
  • Aiport fire crews entered the cabin with a fire hose to help fight the fire,
  • Flight attendants helped to fight the fire with fire extinguishers, and also used the extinguishers to help extract the two flight attendants who were trapped by the two escape slides that deployed inside the cabin.

Cabin damage
Prior to the cabin fire, a firefighter entered door 2L and turned right to walk toward the rear of the cabin, and along the way observed that seats in that section were almost pristine, with minimal damage detectable, and that one could just fluff the pillows to get that section ready for the next flight. As he walked toward the rear, he observed more cabin damage, with a sharp contrast between the front and back of the passenger cabin. The photo below shows the pristine area of the cabin that was later damaged by fire.

(click to enlarge)

The NTSB structures team noted that from the cockpit to rear spar of the center wing box, the cabin floor was structurally sound. Aft from the rear spar to doors 3R and 3L, in the passenger seating compartment, support structure were compromised on the right side (flayed out from the aircraft), but still sound on the left side. Between doors 3 and 4, the floor was canted down at an angle, with damage progressively worse towards the back, and there was no cabin floor behind door 4.

Dr. Curtis and Capt. Tom Bunn discuss the crash
The day after the crash, Dr. Curtis of and Capt. Tom Bunn of the SOAR fear of flying program, who both spent several hours on the day of the crash on cable news programs providing expert commentary, discussed the media's response to the accident and shared their thoughts on the early reports of the crash.

Additional information 10 July 2013 article on the role of the autothrottle 8 July 2013 article on early findings of the crash investigation
Other Asiana plane crashes
Other 777 plane crashes
Accident details from Aviation Safety Network
Wikipedia page on this accident

Photos: Wikipedia, NTSB

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