I thought it perhaps worthwhile to post the following from the 738 reject report, as it highlights the difficulties faced in the decision making process at an extremely critical time.
http://www.onderzoeksraad.nl/docs/ra...yan_Air_EN.pdf
REJECTED TAKEOFFS IN A HISTORICAL PERSPECTIVE
Rejected takeoffs are not uncommon and in the past have resulted into accidents. Several studies and investigations were performed on rejected takeoffs, a general overview of these studies will follow. In 1990 a Special Investigation Report Runway Overruns following high speed rejected takeoffs was published by the National Transportation Safety Board (NTSB) of the United States of America. The NTSB conducted this investigation to determine how the safety of rejected takeoffs could be enhanced and the rate of incidents reduced. The investigation used a variety of information on rejected takeoffs including historical accident data and airline procedures. In this special investigation report several recommendation are made to the Federal Aviation Administration (FAA) on improving safety for rejected takeoffs. An overview of the recommendations are presented in appendix H. In 1994 the FAA in a joined effort with industry created a training tool for rejected takeoffs, the Takeoff Safety Training Aid. The main purpose of this training tool was to reduce the number of rejected takeoffs by improving flight crew decision making process, knowledge and awareness. The Takeoff Safety Training Aid describes the background of events and lays down training methods and simulator scenarios for pilot training on rejected takeoff decision making. The “Takeoff Safety Training Aid” training program is designed to facilitate flight crews in reaching and maintaining proficiency in:
• Recognising and understanding situations and factors that make high speed rejected takeoff decisions critical.
• Making appropriate Go/No Go decisions.
• Executing rejected takeoff procedures and employing techniques that maximises the stopping capability of the airplane should a high speed rejected takeoff be necessary.
• Continuing the takeoff safely should that be deemed the most appropriate course of action. In this safety training aid, data and background information on rejected takeoffs from 1959 up to 1990 is presented. It is reported that 76% of all rejected takeoffs are initiated at speeds of 80 knots or less. The rejected takeoffs at low speed almost never result in an accident. About 2% of the rejected takeoffs are initiated at speeds above 120 knots. Statistically more than half of the runway overruns or excursions have occurred when the rejected takeoffs were initiated at high speeds (greater than V1).
REJECT SPEED
80 knots or less 76%
80 – 100 knots
x 18%
100 – 120 knots
x 4%
Above 120 knots 2%
According to the Takeoff Safety Training Aid in the event the airspeed is beyond V1 a “go decision” is less hazardous and the takeoff should therefore not be rejected. The reasoning is that the problem faced by the flight crew may be handled more safely as an in-flight problem than a high speed rejected takeoff. The reasons for rejecting a takeoff vary from an indicator/light to wheel or tire failure.
REASONS FOR REJECT
Engine
xxxxxxxxxxxxxxxxx24.3%
Wheel/Tyre
xxxxxxxxxxxx22.9%
Other and not reported 13.5%
Configuration
xxxxxxxxxx12.2%
Indicator/Light
xxxxxxxxxx9.5%
Crew Coordination
xxxxxxx8.1%
Birdstrike
xxxxxxxxxxxxxxx6.8%
ATC
xxxxxxxxxxxxxxxxxxxx2.7%
In an advisory circular AC no: 120-62 the FAA recommends the use of the Takeoff Safety Training Aid to operators. It is recommended that the training aid is incorporated in the operators flight crew training and qualification programs of operators. FAA inspectors are required to check the operators manuals and training to asses if the Takeoff Safety Training Aid is used and guidelines are followed. In 2004 the pilot guide to takeoff safety (section 2 of the training aid) was updated. The study period was extended from 1959 up to 2003 and accident data was supplemented with 25 additional rejected takeoffs. The additional data showed that the rate of rejected takeoff decreased. The engine related rejecting takeoffs decreased and wheel/tire failures increased by a small percentage. In late 2006, the Flight Safety Foundation initiated a project entitled Runway Safety Initiative (RSI) to address the challenge of runway safety. An in-depth study was conducted of all runway excursion accidents from 1995 through March 2008 to investigate the causes of runway excursion accidents and to identify the high-risk factors. Data was analysed to identify the most common risk factors, both in takeoff excursions and landing excursions. The most common risk factor in takeoff excursions was a rejected takeoff initiated at a speed greater than V1. Loss of pilot directional control was the next most common, followed by rejecting the takeoff before V1 was reached. This study concludes that a mishandled rejected takeoff increases the risk of takeoff runway excursion. Operators should emphasise and train for proper execution of the rejected takeoff decision and training should emphasise recognition of takeoff rejection issues. Furthermore Cockpit Resource Management and adherence to Standard Operating Procedures are essential in time-critical situations such as rejected takeoffs. A recent study (2010) by the National Aerospace Laboratory, in the Netherlands compared rejected takeoff events for the period 1980-1993 with the period 1994-2008. The split 1993-1994 was chosen because in 1994 the Takeoff Safety Training Aid was introduced. The NLR study shows that the occurrence rate of rejected takeoffs in general has decreased, however the rate of high speed rejected takeoffs has not changed. In the NLR study the decision to reject a takeoff is also examined. The study shows that the correctness of the decision to reject a takeoff before and after 1994, the introduction of the Takeoff Safety Training Aid, has not increased. The statistical information on the correctness of the decision to reject a takeoff is based on hindsight. Pilots at the time thought they were making the right decision. The study concludes that especially in complex situations, for example a combination of engine failure with significant vibration, it is difficult to assess. Assessing a complex situation and deciding to reject the takeoff is also not well trained. The study points out that the lack of reference as to what might make the aircraft unsafe to fly makes it difficult for crews in recognising such a situation to make an appropriate decision. It should be noted that care must be taken in comparing the positive (yes) and negative (no) decision to reject the takeoff. The undetermined reasons of correctness of the decision has increased in the period 1994-2008 versus 1980-1993.
REJECTED TAKEOFF DILEMMA
In the past industry initiatives and studies have identified that rejected takeoffs are a high risk area. Analysis of available data highlighted that after V1 and VR a runway overrun is likely and could potentially result in aircraft damage and/or loss of life. Statistics further show that the rate of rejected takeoff is declining. However the rate of high speed rejected takeoffs is not. In general past studies conclude that if procedures were followed the outcome would have been different. This conclusion it subsequently followed by the recommendation that flight crew should follow procedures and act accordingly. Despite simulator training on rejected takeoffs and instruction on the risks of (high speed) rejected takeoffs flight crews, when faced with a problem in reality, do not always react desirably and follow procedures. This is mainly due to the fact that during takeoff the interaction between the aircraft, environment and crew are tightly related. This interaction may result in a complex situation which is unfamiliar and difficult to assess. Technical monitoring and warning system were introduced into aircraft in the past which, when appropriate, would warn flight crew of a problem. This warning system monitors aircraft condition and should help flight crew in assessing situations correctly. In this event no warnings were triggered and the aircraft did not indicate there was a problem. From a manufacture standpoint the aircraft was therefore airworthy and safe to fly. The control check performed before flight is, in part, to assess the aircraft state and verify control responses. The environmental conditions like snow and rain on a runway are addressed in manuals to help flight crew in determining aircraft performance and make adjustments. This information is used to set preconditions and determine decision speeds. The fact remains that despite aircraft monitoring and managing preconditions impacting aircraft performance unexpected situation may occur. On takeoff the flight crew rely on perception and interpretation of situations. This perception and interpretation provides opportunity for errors in decision making. Guidance, procedures and training should help pilots in the decision making process in the critical phase of flight. With the current state of technology and human factors theories available, a re-evaluation of the rejected takeoff concept and procedures may be useful and warranted.