Stilton;
Unlike on older Aircraft where we trained to use the all stopping devices to their maximum potential as routine the 'relegation' of reverse thrust to a minor role can lead to an underestimation of it's importance when needed.
I have had to very assertively 'encourage' a few Pilots to get max reverse stuck in early when it's most effective on short / wet runways when it's really needed.
This is even after briefing the requirement prior to the approach. Can't blame them because it has ceased to be part of the normal 'muscle memory'
From the ATSB Accident Report on the QANTAS B747-438 over-run accident at Bangkok, September, 1999, regarding use of reverse thrust, reduced landing flap and use of FOQA data:
The absolute rates of both QAR events listed in table 8 were low. However, statistical analysis indicated that there was a significant difference in the number of alerts for parameter 161 before and after the flaps 25/idle reverse procedures were introduced (December 1996). The exact reasons for the increase in parameter 161 alerts could not be determined. It is unlikely there was a general change in environmental conditions after December 1996 that resulted in a noticeable increase in the rate of alerts, and was then maintained at a higher level. However, due to the timing of the change, it is reasonable to conclude that the use of flaps 25 (rather than flaps 30) was one of the issues involved. Although the actual flap configuration used on each occasion could not be verified, it is reasonable to conclude, based on the information in section 1.7, that flaps 30 was used almost exclusively before December 1996 and flaps 25 was used predominantly after 6 December 1996. Regardless of the actual reasons for the increase in 161 alerts, the company’s monitoring of QAR data had not detected the increase. The company did not use QAR information to proactively monitor the possible influence of the flaps 25 procedure, and it had not systematically evaluated QAR data using formal statistical methods before the accident. Had it conducted such activities, the increased frequency of high-speed approaches would probably have been detected. The exact reasons for the increase could then have been investigated.
In mid-1999, two senior pilots expressed concern to the Manager B747-400 Training and some other managers that, in certain situations, some first officers did not appear to be considering flaps 30 and full reverse as intelligent options when conducting approach briefings. This issue was raised during the B747-400 training staff meeting in May 1999, and check-and-training staff were asked to ‘encourage and develop airmanship’ in this area. This instruction was recorded in the minutes of the meeting, which were available to all B747- 400 check-and-training personnel. However, during the investigation, a number of checkand- training personnel stated that they could not recall the issue being discussed.
Risk assessment of the flaps 25/idle reverse procedures
In a broad sense, Flight Operations Branch was aware that the risks associated with the flaps 25/idle reverse procedures needed to be considered in its evaluation of the proposal. The prime factors considered during the review process (see attachment H) were that flaps 25 was a certified flap setting, that the landing data did not include the use of reverse thrust, and that some other major airlines had adopted similar procedures. Some personnel considered that the decision to implement the new procedure would probably have not been any different had a formal risk assessment been conducted.
In attachment H, the conclusion is drawn that the informal risk assessment process used by the company in evaluating the flaps 25 and idle reverse proposals contained several
weaknesses. These included:
• There is no evidence that Qantas had sought Boeing’s opinion regarding the safety impact of the new procedures and their potential effect on carbon brake wear. Management personnel agreed that Boeing’s opinion on such issues would be useful, and that they would normally consider the manufacturer’s opinion before changing procedures. Boeing has since stated that it does not support the use of idle reverse thrust as a normal procedure as it increases landing distance. It has also stated that modified braking techniques alone would produce almost as much reduction in brake wear as the combined effect of the flaps 25/idle reverse procedures.
• Qantas examined the flaps 25/idle reverse procedures of two other operators as part of the project development process. This examination was incomplete and did not identify that the procedures used by these operators were more conservative than the proposed Qantas procedures, and had additional safeguards in place for operating on wateraffected runways (see airlines D and E in attachment I).
• The performance differences between idle and full reverse thrust, and between flaps 25
and flaps 30, were not fully examined. Such an examination would probably have highlighted the significant differences in landing distance on wet or contaminated runways using these various configurations.
• There is no evidence that a systematic attempt was made to identify all the situations for which flaps 30 and/or full reverse thrust would be more appropriate.
• The term ‘contaminated’ was used in the flaps 25 procedure but was not defined.
• There appears to have been no review of the human factors implications of the new procedures. For example, there appears to have been no consideration of the extent to which the use of flaps 25/idle reverse could become a skill-based habit (i.e. ‘ the norm’), and therefore might be used by crews when a more conservative configuration was required. As discussed in section 3.1.2, two senior personnel reported problems with the training of flaps 25/idle reverse procedures in mid-1999. However, there is no evidence that any followup action was obtained to assess the significance of this potential hazard.
Observations:
The Flight Operations Branch did not have in place a systematic process for assessing identified risks in its operations. The process of using expert judgement at a series of independent levels probably ensured that most problems associated with new procedures were identified, analysed and evaluated. The shortcomings in the development of the flaps 25/idle reverse procedures clearly indicated the limitations of relying on an informal process.
The approach outlined in AS 4360:1999 is highly desirable.