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Singapore Airlines 327

Accident Case Study

The only airplane I've ever flown with an autoland capability was the Air Force Boeing 747, and back then in the 1980s, the autoland system was so inconsistent that we were reluctant to use it, even though we were required to use if for currency. We did our training with United Airlines and heard their pilots would "pencil whip" the event because they didn't want to take the risk or have the airplane make them look bad. The aircraft became noncurrent. When the Boeing 767 came on line a curious thing happened. Their pilots preferred to have the airplane autoland; it did such a good job that it made them look good. the pilots became noncurrent. That was almost 30 years ago. We are now at the point where many operators, including this one, recommend the autoland whenever the ceiling or visibility are even moderately low.


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Photo: Singapore Airlines 327, aircraft position after stop, BFU EX010-11, p. 26

Click photo for a larger image

Accident Report

  • Date: 3 November 2011
  • Time: 1209 LT
  • Type: Boeing 777-300 ER
  • Operator: Singapore Airlines
  • Registration: 9V-SWQ
  • Fatalities: 0 of 15 crew, 0 of 147 passengers
  • Aircraft fate: Minor
  • Phase: Landing
  • Airport (departure): Manchester International Airport, United Kingdom (EGCC)
  • Airport (arrival): München-Franz Josef Strauss Airport, Germany (EDDM)

Narrative

The report says these pilots were surprised when the autopilot dipped a wing in the flare, deviated left after touchdown, and did not execute the go-around when commanded. I think they may have never seen the system misbehave before and had become complacent to the need to monitor the system, especially during the landing.

The autoland system I flew years ago in the Boeing 747 was primitive by comparison but would have behaved the same way. I have been in the flare during a practice Cat IIIA ILS approach, intending to let the system land the airplane, when a similar thing happened. The aircraft started to roll fairly aggressively. I disengaged the autopilot and landed manually. This pilot attempted to do that using the autopilot's go-around function. But they were already on the ground and the go-around function was no longer enabled.

[BFU EX010-11, ¶1.1]

  • On 1 November 2011 the crew had conducted the flight from Singapore to Munich. After a 48-hour stay, on 3 November 2011, the crew conducted the flight from Munich to Manchester and back. Both pilots stated they had slept well, felt rested, and almost adjusted to Central European Time (CET). At 0515 hrs the crew reported for duty. The flight to Manchester occurred without incident. On the subsequent return flight to Munich 147 passengers, 13 flight attendants and 2 pilots were on board.
  • According to crew statements the co-pilot was initially Pilot Flying (PF) during the flight Manchester - Munich. Based on the latest weather information at Munich, visibility 2,000 m, cloud base 300 ft, the Pilot in Command (PIC) decided to assume the role of PF, as the SOPs (FCOM/NORMAL PROCEDURES/OPERATION) of the operator required, and the co-pilot became Pilot Monitoring (PM).
  • The weather was IFR (300 ft ceiling and 1-1/4 mile) and as their SOP required the captain to take the landing, this decision makes perfect sense.

  • The PIC decided to conduct an automatic approach and autoland.
  • The company operations manual recommended using an autoland under these conditions.

  • As the B-777 was about 50 ft above the runway in the flare phase the airplane began to slowly bank left up to 3.5°. The PIC called out: “Okay, flaps twenty.”
  • This call coincided with the PF hitting the Takeoff/Go-Around (TO/GA) switch. The "Okay, flaps twenty" was not according to airline SOP, and the PM did not move the flap handle.

  • At approximately 420 m beyond the runway threshold the airplane touched down with the left main landing gear and 132 kt (KIAS). At that time the Auto Flight System (AFS) switched to rollout mode.
  • The autopilot was still engaged as the airplane moved toward the left runway edge and veered off the runway with a speed of 123 kt (KIAS) about 944 m beyond the threshold in the area of taxiway B4. For about 400 m the airplane rolled through the grass north of runway 08R in a slightly curved right hand turn. The largest lateral deviation from the runway was reached at about 1,242 m beyond the threshold; speed was 109 kt KIAS. Because of the system design the autopilot disengaged due to crew inputs via the rudder pedals. The airplane turned right by about 40°, re-entered the runway close to the intersection with taxiway B6, about 1,566 m beyond the threshold. The aircraft crossed the runway with a heading of about 120°. Speed was still 71 kt KIAS. The airplane veered off the runway again, turned left by about 40°, and came to a stop in the grass south of and parallel to runway 08R. At 1209:09 hrs the airplane crossed the threshold; at 1209:51 hrs it came to a stop.
  • Video: Singapore Airlines 327.

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Photo: Photo: Singapore Airlines 327, rolling traces of the airplane, BFU EX010-11, p. 27

Click photo for a larger image

[BFU EX010-11, ¶1.11] At 1207:53 hrs as the B 777 was about 2.9 NM ahead of the threshold of runway 08R, one aircraft each was at the CAT II/III holding position of taxiways B1, B2 and B3 and two aircraft were farther north of them. An additional airplane taxied west on taxiway S. At the same time a BAE 146-RJ85 taxied over the high speed taxiway B4 onto runway 08R and started the take-off run about 20 seconds later. At that time the B 777 was about 2.1 NM prior to the runway threshold in an altitude of about 700 ft AMSL. At 1209:09 hrs the B 777 crossed the threshold of runway 08R in an altitude of 50 ft. Six seconds later the BAE 146-RJ85 overflew the end of the runway in about 380 ft. At 1209:29 hrs the BAE 146-RJ85 overflew the ILS localizer antenna of runway 08R in 740 ft.

Analysis

When is the ILS critical area (sometimes called "sensitive area") protected? It depends on where you are. We pilots want it protected whenever we are landing in instrument conditions. Air traffic control doesn't like doing that because it decreases the number of airplanes they can have land and takeoff as well as operate on the ground. In this case, the preceding takeoff had not yet flown beyond the localizer antenna when the accident airplane was in the flare. The spacing ending up being insufficient.

[BFU EX010-11, ¶1.6.]

  • The autopilot flight director system can detect ILS signal interferences which are caused by vehicles or aircraft on the ground. In such cases the autopilot disregards the ILS signals and switches in the attitude stabilizing mode which is based on data from the on-board inertial navigation system. These interferences generally only last for short periods of time and no error is indicated. If the interferences last longer the flight director mode is downgraded from LAND3 or LAND2, for example.
  • Flare Mode. During an autoland the airplane in flare mode is guided toward the ground in a slight flare curve. The flare mode is only active if the PFD indicates LAND2 or LAND3 and starts about 50 ft above the runway. Between 50 ft and 25 ft the thrust levers are automatically pulled into idle. On the PFD the indication changes from SPD to IDLE. After touch-down of the nose landing gear on the runway the indication on the PFD changes from Flare into Rollout Mode.
  • Rollout Mode. The rollout mode is armed when the airplane is at about 1,500 ft radio height and becomes active once the aircraft is below 2 ft above the runway. After touch-down the autoflight system uses rudder and nose wheel steering to follow the localizer signal.
  • Go-Around Mode. The automatic go-around mode is on stand-by when the flaps are beyond their neutral position or the ILS glide slope is activated. The automatic go-around becomes active once one of the two push switches on the thrust levers (TO/GA button) is pushed. The manufacturer stated that the go-around mode is deactivated when the AFDC logic signals that the airplane is on the ground. This logic takes into account the radio height and the Weight on Wheels (WOW) signal from the Air Ground Indication System (AGIS). The autopilot calculates the height of the landing gear based on the radio altitude and the aircraft geometry. The calculated landing gear height has to be less than 2 ft and the left or right WOW signal has to be present.
  • It appears the go-around mode was deactivated when the PF hit the TO/GA button, since once of the landing gear was on the ground.

    [BFU EX010-11, ¶1.8.2.1.]

  • Basically electromagnetic waves propagate in a straight line. This can be affected by:
    • Refraction - is the change in direction of a wave due to a change in its transmission medium (while propagating in an inhomogeneous medium it is bend toward the denser area).
    • Diffraction - waves are bend around edges.
    • Diffusion - radiation originally propagating in one direction is being diffused by an object and then propagates in different directions.
    • Reflection - whenever radiation meets a plain or slightly bent surface it is being refracted (like a mirror).
  • Interference Sources. Surfaces and edges of objects affect the propagation of electromagnetic waves. Metallic surfaces have a special importance due to their electromagnetic characteristics.
  • Objects in the area of the extended runway centre line are directly in the propagation path from the localizer antenna to the approaching or rolling-out aircraft.
  • Outside the course sector full scale deflection of the course deviation indicator is required and in order to ensure it, electromagnetic energy is also radiated in areas which are further away from the extended runway centre line.
  • Sources of interference can therefore be:
    • Buildings such as terminals, hangars, antenna support and masts
    • Aircraft and other vehicles on the ground
    • Aircraft flying ahead in the area of the approach path or above the approach path.

[BFU EX010-11, ¶1.17.1.1.] In accordance with the guidelines for all-weather operations (NfL I/1-99 in combination with NfL I/188-10) Low Visibility Procedures (LVP) are applied when the following conditions prevail: a Runway Visibility Range (RVR) of less than or equal to 600 m and/or a cloud base of 200 ft. Under the above-mentioned conditions and as soon as the approaching airplane is within 2 NM ahead of the runway threshold, the separation between an approaching aircraft and another approaching or departing airplane has to be such that the ILS signals will not be distorted by departing or approaching aircraft. Item 5.7.2 of the NfL stipulates that during approaches (also trainings) under better weather conditions than CAT II or CAT III the pilot has to specifically request the application of all-weather operations on the ground if the higher (more restrictive) category is desired. The air traffic control unit informs the pilot if and with which restrictions all-weather operations on the ground can be conducted. The stipulations published in the guidelines for all-weather operations are in accordance with the Manual of Operations Air Traffic Services (MO-ATS) of 2011.

[ICAO Doc 9365, ¶3.2.21] In addition to critical areas, sensitive areas associated with a facility must be protected if the weather conditions are lower than 60 m (200 ft) cloud base or 550 m RVR when instrument approach operations are being carried out. In the latter case, aircraft which will overfly the localizer transmitter antenna after take-off should be past the antenna before an aircraft making an approach has descended to a height of 60 m (200 ft) above the runway; similarly an aircraft manoeuvring on the ground, for example when clearing the runway after landing, should be clear of the critical and sensitive areas before an aircraft approaching to land has descended to a height of 60 m (200 ft) above the runway. The protection of these areas when the weather conditions are better than the minimum specified above will facilitate the use of automatic approach and landing systems and will provide a safeguard in deteriorating weather conditions and when actual weather conditions are lower than reported.

[AIM, ¶1-1-9.k.2.] ATC issues control instructions to avoid interfering operations within ILS critical areas at controlled airports during the hours the Airport Traffic Control Tower (ATCT) is in operation as follows: (a) Weather Conditions. Official weather observation is a ceiling of less than 800 feet and/or visibility 2 miles.

The current weather was visibility 2,000 m (1-1/4 miles) and 300 feet. Under U.S. rules, the ILS critical area would have been protected; but under ICAO and German rules, the area was not protected.

[BFU EX010-11, ¶1.17.2.1.] Flight Crew Operation Manual (FCOM) Normal Procedures / Operation. An autoland is recommended if the following weather conditions exist:

  1. Cloud Base at or below 500 ft AAL, or
  2. Visibility of 2 km or less, or
  3. Any time RVR is quoted.

[BFU EX010-11, ¶2.2.]

  • The crew did not inform the approach controller of their intention to conduct an automatic landing.
  • The crew knew that under the prevailing CAT I flight operations the safety measures of all-weather operations CAT II/III were not present.
  • Even though the PIC’s command “Okay, flaps twenty.” did not completely meet the requirements of the standard phraseology for a go-around “Go-Around Flaps 20” it was his command to go-around. The analysis of the FDR showed that the co-pilot did not set the flaps to 20°.
  • The FDR analysis in combination with the sonogram indicates that the TO/GA button was pushed simultaneously with the initial ground contact of the left main landing gear. The crew anticipated that the Go-Around Mode would initiate a go-around, but nothing happened. The Go-Around Mode had deactivated as designed by Boeing (system logic) by the initial ground contact of the main landing gear.

[BFU EX010-11, ¶3.1]

  • A BAE 146-RJ85 taxied along taxiway B4 to runway 08R as the B 777 was about 2.9 NM ahead of the runway threshold 08R and 3.4 NM behind the BAE 146-RJ85 when it received take-off clearance.
  • As the B 777 flew above the runway threshold 08R, the BAE 146-RJ85 was in front of the localizer antenna and interfered with the localizer signal.
  • The BAE 146-RJ85 was significantly lower in front of the localizer antenna compared to other airplanes having taken off earlier due to it taken off from the taxiway B4 intersection and its lower climb rate. This resulted in a significantly greater localizer interference.
  • The B 777 followed the disturbed localizer signal with engaged autopilot.
  • The crew realised the interference too late and was confused by the deviation of the airplane to the left.

Cause

I think the intent of the report writers was good, however I would have gone a bit further. The operator should have instilled a health dose of paranoia in their pilots when using the autoland system, especially in conditions where the ILS critical area was not protected.

[BFU EX010-11, ¶3.2] The recommendation concerning the conduct of autoland landings under CAT I conditions published in the FCOM of the operator allowed the decision for an autoland landing without having to consider the required conditions on the ground.

Sea also:

Paranoia

Stick and Rudder in an Age of Ones and Zeros

References

Aeronautical Information Manual (AIM)

Bundesstelle für Flugunfallentersuchung (BFU) German Federal Bureau of Aircraft Accident Investigation, BFU EX010-11, Boeing B777-300ER, Singapore Airlines, Munich, 3 November 2011.

ICAO Doc 9365 - Manual of All Weather Operations, International Civil Aviation Organization, Third Edition, 2013

Revision: 20170915
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