Titan B733 at Chambery on Apr 14th 2012, tail strike
Last Update: April 12, 2013 / 15:05:59 GMT/Zulu time
Incident Facts
Date of incident
Apr 14, 2012
Aircraft Registration
G-ZAPZ
Aircraft Type
Boeing 737-300
ICAO Type Designator
B733
The use of computers in the calculation of performance requirements has brought about improvements in the accuracy and ease with which they can be made. There remains, however, a continued vulnerability to the use of incorrect data in making these calculations, a solution to which remains outstanding. This accident serves to demonstrate that, given these circumstances, the existence of and adherence to robust procedures, and appropriately designed software and hardware, are essential.
This event once again emphasises the need for technical solutions for takeoff performance monitoring, to cater for those occasions where current safeguards have failed, and reiterates previous Safety Recommendations made by the AAIB on this issue.
The AAIB reported that the crew used the electronic flight bag for takeoff computations. Their first flight of the day was the positioning flight from London Gatwick to Chambery without passengers. 131 passengers boarded the aircraft in Chambery in addition to the 5 crew already on board. During flight preparations the captain (34, ATPL, 3,950 hours total, 1,417 hours on type), pilot flying, entered the Zero Fuel Weight from the load sheet into the flight management computer, which the FMC subsequently converted to the takeoff weight, which seemed reasonable.
The crew subsequently computed takeoff performance using their electronic flight bag (EFB) computers again, due to the critical takeoff performance the system recommended a takeoff at flaps 1 and came up with speeds that seemed reasonable. The captain inserted those speeds into the FMC manually overwriting the values that the FMC had computed. The captain said in post flight interviews that he had not noticed any significant differences. The EFB had also computed a reduced thrust takeoff was possible, the crew preparted for the reduced thrust takeoff.
The aircraft subsequently departed Chambery's runway 36. During takeoff acceleration the flight crew felt a slight judder that they believed was the result of wake turbulence of the previous departure. During initial climb the flight crew received a call from the aft cabin, intended to call the purser but mistakenly calling the cockpit, informing the flight crew, the flight attendants in the back cabin had felt that judder as well. The pilots assured this was just turbulence. The flight was continued to London, where the aircraft landed.
After landing at Gatwick Airport ground personnel informed the flight crew about abrasions to the aircraft tail, which prompted the flight crew to review their takeoff computations. They discovered that they had not inserted the takeoff weight (52900kg) into the EFB, which had thus continued to use the takeoff weight (46300kg) for the positioning flight from London to Chambery, about 6,600 kg/14,500lbs short of the actual takeoff weight. The crew had thus received V1=118 knots, Vr=127 knots and V2=140 knots, whereas the correct values would have been V1=129 knots, Vr=139 knots and V2=149 knots.
The flight data recorder showed that rotation was initiated at 126 KCAS, approximately 4 seconds later the pitch attitude increased through 10.8 degrees at which tailstrike would occur. The aircraft reached correct V2 (149 knots) at 30 feet above ground.
The aircraft received deep longitudinal scoring of the rear fuselage skin, about 1.9 meters in length, lateral damage occurred to two stringers. Due to the complete abrasion of the fuselage skin supporting fuselage frames also received abrasions creating a leak path for the pressurized cabin air though the path and leak rate was insufficient to affect cabin pressurization during the flight to London Gatwick.
The AAIB analysed that after the takeoff computation at London had been conducted, the EFB had been put into standby, which would turn off the display but keep the actual software running retaining the values entered. The operator stated this was useful as it enabled the crew to quickly recompute takeoff performance in case of last minute changes. However, the operations manual did not require crew to shut the EFB down between flights, thus it was possible that takeoff data of a previous takeoff were retained and not requested for current takeoff.
The EFB as well as the checklists, including the non-management of data retained from previous takeoffs, had been approved by UK's CAA.
The AAIB further stated that a similiar situation in retaining the data of the previous takeoff led to the crash of a Boeing 747 registration 9K-MKJ in Halifax in 2004, the Canadian TSB had recommended: "Any field in the performance application which is used to derive operational performance for a critical phase of flight from remaining populated after the EFB is shut down."
Another similiar occurrence happened in 2009, see Accident: Emirates A345 at Melbourne on Mar 20th 2009, tail strike and overrun on takeoff prompting the ATSB to recommend: "While it is likely that these errors will continue to take place, as humans are fallible, it is imperative that the aviation industry continues to explore solutions to firstly minimise the opportunities for take-off performance parameter errors from occurring and secondly, maximise the chance that any errors that do occur are detected and/or do not lead to negative consequences."
The AAIB thus released two safety recommendations reading:
"It is recommended that the Civil Aviation Authority update their criteria for the operational approval of Electronic Flight Bags (EFBs) to ensure operators have procedures in place for the use of any ‘standby modes’ and on-screen keyboards, and to prevent the inadvertent use of outdated EFB performance data."
and
"It is recommended that the European Aviation Safety Agency establish a set of detailed guidelines for the operational evaluation and approval of Electronic Flight Bags. These should be more specific than the proposed Acceptable Means of Compliance (AMC) 20-25 and include information such as provided in the Federal Aviation Authority document ‘Electronic Flight Bag Authorization for Use’ and Joint Aviation Authorities Safety Information Communication No 7."
Incident Facts
Date of incident
Apr 14, 2012
Aircraft Registration
G-ZAPZ
Aircraft Type
Boeing 737-300
ICAO Type Designator
B733
This article is published under license from Avherald.com. © of text by Avherald.com.
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