Air France A343 near Guadeloupe on Jul 22nd 2011, rapid climb and approach to stall in upset
Last Update: November 2, 2012 / 08:17:45 GMT/Zulu time
Inadequate monitoring of flight parameters, which resulted in the crew not noticing the autopilot had disconnected and a deviation from assigned altitude after reflex actions at the controls.
Contributing factors were:
- the aural alert "Autopilot Disconnect" was not heard because the simultaneous aural alert "Overspeed" had priority
- the turbulence experienced at the beginning of the upset made reading the instruments difficult
- the "severe turbulence checklist" item to verify whether the autopilot was still engaged was not carried out
- inappropriate use of the weather radar permitted entry into a zone of turbulence
The captain (48, ATPL, 23,226 hours total, 3,081 hours on type) was pilot flying, the first officer (50, ATPL, 9,647 hours total, 2,410 hours on type) was pilot monitoring.
During climb, at about FL180, both crew members adjusted their navigation displays to a range of 320nm, the weather radar was set to maximum gain and a tilt angle to alternate between -0.5 and -1.0 degrees.
The aircraft was enroute at FL350 and a speed of 0.83 mach about 2nm after passing N18 W60 the aircraft entered a zone of moderate turbulence, an "OVERSPEED" aural alert sounded and the master warning illuminated. The airspeed had increased to 0.87 mach. The flight data recorder revealed that the pilot monitoring pressed the autopilot disconnect button, no aural alert sounded, and pulled the side stick about 75% of its travel back for about 6 seconds. The aircraft subsequently rolled right and left indicative that the pilot not flying was not aware of his actions. The airspeed reduces to 0.84 mach, the overspeed warning stops briefly for two seconds, activates again for a second, then silences. At this time the aircraft climbs at a vertical speed of 1950 feet per minute. The master warning stops a second later. The crew selected mach 0.76 for about 3 seconds, then mach 0.85, the spoilers were extended. The airspeed reduces.
The pilot flying reported that as reaction to the turbulence encounter he activated the landing lights in order to be seen and see, he noticed there was rain outside. He then wanted to take the handset for an public announcement but dropped the hand set. The pilot monitoring retrieved the handset and made the announcement to the passengers.
The pitch attitude in the meantime increased from 3 to 9 degrees in 5 seconds, and the aircraft climbed through 35,200 feet. The crew reported later they did not hear the altitude alerter that sounds upon deviating 200 feet from the assigned altitude, the spoilers begin to automatically reduce, 10 seconds after the begin of the upset the aircraft climbed through FL360, the spoilers fully retracted, the pitch angle reached 12 degrees nose up, the mach decreases. The pilot flying noticed the decreasing speed and selected Mach 0.93, the aircraft still climbs, the vertical speed increases through 5700 feet per minute, the crew does not notice the excessive climb rate, engine N1 is at 100%, the pilot flying switches his navigation display to a range of 160nm.
29 seconds after the upset began, the aircraft was climbing through 36,900 feet, the pilot monitoring noticed the master warning had illuminated.
44 seconds after the upset, the aircraft was climbing through 37,950 feet, the pilot flying disengaged autothrust and advanced the power levers into the TO/GA detent.
53 seconds after the upset began the aircraft reached its maximum altitude at 38,185 feet at a mach speed of 0.66.
The pilot flying realizsed at that point they were at 38,000 feet and queried the pilot not flying whether they weren't assigned to FL350.
78 seconds after the upset began the aircraft descended through FL370, the pilot flying pulls the altitude select button on the master control panel which activates the open descend mode on the flight directors. The pilot wants the autopilot to reacquire FL350, but notices nothing is displayed on the primary flight display. The airspeed is 226 knots, 19 knots below the minimum selectable airspeed. Both flight directors are then withdrawn from the displays.
At this time the pilot not flying performed a HF transmission with New York Oceanic Center to inform abotu the altitude deviation and turbulence encounter.
102 seconds after the upset began, the aircraft was descending through 36,500 feet, the pilot flying finally notices the autopilot had disconnected and begins to operate his side stick. The pitch angle subsequently stabilizes, while descending through 35,400 feet the autopilot gets reconnected, the aircraft levels off at FL350, autothrust gets reengaged and the aircraft stabilizes.
Air France Operations Center sent an ACARS message about 5:15 minutes after the upset began indicating that there was nothing visible around N18 W60 on a satellite image and there was no clear air turbulence forecast as well.
The aircraft continued for a safe landing in Paris about 7.5 hours later.
The BEA reported the weather briefing available to the crew showed no significant weather phenomen along their route. This however stood in contrast to infrared satellite images which showed the presence of isolated cumulonimbus clouds of moderate intensity around N18 W60 with tops reaching up to FL380. The trajctory of the aircraft took the aircraft in close vicinity of those clouds.
The BEA analysed that Airbus recommends the use of weather radar tilt angles depending on range settings, to detect water in the air in a distance of 320nm the tilt angle is to be set to -1.0 degrees, for 160nm the tild angle should be set to -1.5 degrees, for 80nm -3.5 degrees and for 40nm -6 degrees. With a tilt angle of -0.5 degrees the weather radar beam would not hit a zone of high reflectivity meaning the probability of a return depicted on the navigation display is low.
Analysis of the flight data showed that the autopilot would have remained connected throughout the event had it not been disconnected manually, the autopilot would have corrected the overspeed keeping the aircraft below or at 35,200 feet.
The overspeed warning has highest priority and results in a master warning that can not be cancelled. The cavalry charge indicative of the autopilot disconnect was therefore suppressed as was the altitude alert. The BEA annotated that on newer aircraft like the B787 or A388 the autopilot calvary charge (aural alert) continues to sound until it is cancelled by a pilot other than on the A340, the autopilot disconnect aural alert therefore would have sounded as soon as the overspeed condition terminated.
The BEA released safety recommendations to improve pilot training for monitoring flight parameters during turbulence or overspeed conditions and for operating the weather radar.
The BEA released another safety recommendation to EASA to require the autopilot disconnect aural alarm become continuous until cancelled by human action, reasoning that the A340 cavalry charge by design sounds 1.5 seconds and may therefore be suppressed by a higher priority aural alert. This suppression had contributed to a critical incident, the BEA continued.
The BEA further demanded the cockpit voice recorder capacity to increase beyond 2 hours in order to store a complete long haul flight arguing that currently capacities of up to 10 hours are readily available at the market and thus should be required.
This article is published under license from Avherald.com. © of text by Avherald.com.
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