The Boeing 717 aircraft was departing Melbourne for Coolangatta on a regular public transport service. Following a normal take-off the pilot in command (PIC), the handling pilot, called for the landing gear to be retracted. A short time later, he noticed an amber warning appear on the airspeed scale on his primary flight display (PFD) screen. The PIC immediately reduced the aircraft pitch attitude in response to that warning. At about the same time, he noticed that the flaps/slats lever was at the `slats retract' position. The PIC immediately called for the flaps to be re-positioned, but the copilot selected the landing gear up. The PIC again called for the flaps to be re-positioned and the copilot then returned the flap selector to the take-off position. The PIC reduced the pitch attitude further. The airspeed then quickly increased to 15 knots above the reference speed (Vref) as the flaps reached the take-off position. The PIC re-established the normal climb attitude and the flaps and slats were subsequently retracted in accordance with the normal profile. The remainder of the flight was uneventful. Both the PIC and the copilot believed that the stick shaker had activated momentarily during the sequence.
Examination of the flight data recorder from the aircraft revealed the following:
- Three seconds after the aircraft became airborne, and at about 30 ft above ground level, the flaps/slats lever was moved from the take-off position and the flaps began to retract.
- One second later, as the flaps/slats lever reached the retract position, the stick shaker warning commenced. At that time the aircraft pitch angle was 18.6 degrees and the computed airspeed was 157 kts. Over the next three seconds, the stick shaker warning continued and the aircraft pitch angle reduced to 10.2 degrees. A second later the landing gear handle was recorded in the up position.
- The flaps/slats lever began to move from the retracted position about one second after the landing gear handle reached the up position. The flaps reached the fully retracted position less than two seconds later, before immediately beginning to extend again. The slats began to retract but did not reach the fully retracted position before moving back to the extended position. The flaps/slats movement was accompanied by a very brief reactivation of the stick shaker and a further reduction in aircraft pitch angle to about 6 degrees. Computed airspeed at that time was 165 kts. The aircraft then began to accelerate and quickly returned to a normal climb profile.
- One altitude loss of 5 feet, and lasting less than three seconds, coincided with the reduction in pitch angle that was made in response to the second stick shaker activation. At that time the aircraft was more than 240 ft above ground level. There was no altitude loss associated with the first stick shaker activation.
Interviews with the PIC and copilot did not reveal any obvious issue that might have led to the copilot retracting the flaps/slats instead of the landing gear. His work schedule, recent life history, and activities leading up to the occurrence were unremarkable. Against that background, the actions of the copilot appear to have been an `action slip', a type of procedural error associated with two actions (landing gear and flaps/slats retraction) that are sequentially linked. As was the case here, in human behaviour there can sometimes be a `spill-over' that triggers the associated action at an inappropriate time.
Primary flight displays are liquid crystal screens that provide attitude, airspeed, altitude, and heading information for each pilot. The airspeed is displayed as a vertical `tape' on the left side of the PFD screen. The aircraft is equipped with a stall warning system that alerts the crew of an `approach-to-stall' condition. The warnings are generated by angle-of-attack, horizontal stabiliser position, and flaps/slats position inputs to the flight control computer (FCC). The FCC displays amber and red sectors (the so-called amber foot/red foot) on the airspeed tape to warn of an `approach-to-stall' condition. The FCC also activates the stickshaker. If the crew does not initiate recovery action, red STALL annunciations appear on the PFDs, a klaxon sounds, and a synthetic voice `stall' warning is activated.
In this occurrence, by reducing the aircraft pitch angle, the PIC responded appropriately and very rapidly to the `amber foot' warning that appeared on the speed tape as soon as the flaps/slats lever was moved from the take-off position. As a result, the aircraft moved from a deteriorating and potentially unsafe flight performance regime to a safe one.
Anecdotal evidence was received early in the investigation that there may have been other inappropriate/inadvertent flap/slat selections in B717 aircraft. As a result, and in cooperation with the operator, a survey was issued to company pilots who flew the aircraft. The survey revealed three other instances of the flap/slats lever being moved through the flaps zero position to the slats retract position. However, all those events occurred above 3,000 feet altitude during initial `clean-up' flap retraction after take-off and the error was recognised and corrected on each occasion. None was associated with landing gear selection after take-off.
In response to the occurrence, the company amended its procedures for flaps/slats retraction approaching the ramp after landing to include the following CAUTION note:
`When retracting flaps/slats to UP/RET, pause at the UP/EXT position until the flaps indicate UP on the PFD prior to retracting the slats. Never move the flap/slat handle to UP/RET in one motion.'
The purpose of the change was to separate the retraction of the flaps and slats into two distinct actions, in an attempt to prevent the retraction of the flaps and slats becoming `learned' as a single continuous action.
|Date:||05 May 2003||Investigation status:||Completed|
|Time:||0735 hours EST|
|Release date:||29 April 2004||Occurrence class:||Operational|
|Report status:||Final||Occurrence category:||Incident|
|Highest injury level:||None|
|Aircraft manufacturer||The Boeing Company|
|Type of operation||Air Transport High Capacity|
|Damage to aircraft||Nil|
|Departure point||Melbourne, VIC|
|Departure time||0735 hours EST|
|Role||Class of licence||Hours on type||Hours total|