On the Design of Flight-Deck Procedures - Intelligent Systems ...

mission simulation (see Wiener et al., 1991). They reported that crews who scheduled their task earlywithin the window tended to be rated as high performing crews. Conversely, crews who scheduled theirtasks late within the window tended to be rated as low performing crews. Laudeman and Palmerconcluded that “scheduling of a task early in the window of opportunity is the optimal task schedulingstrategy” (p. 20). Figure 11 is a graphical depiction of several windows of opportunity in the Laudemanand Palmer study.Altitude(feet)20,000TaskApproach briefingDescent checklistApproach checklistCSD Low oil light proc.Window of OpportunityReceiving ATIS -> 11,00 feetTop of Descent -> 11,000 feet11,000 feet -> Outer MarkerDetecting low oil light -> Outer Marker15,000Approach Briefing & Descent Checklist11,00010,000Abnormal Indication:CSD Low Oil Light5,000ApproachChecklistCSD Low OilProcedure2,1000500 1000 1500Time(seconds)Figure 11. Windows of opportunity during the descent to Columbia, SC.The above findings are applicable in light of a recent airline accident (NTSB, 1991):In 1990 a MarkAir B-737 crashed about 7.5 miles short of runway 14, Unalakleet, Alaska. The captain (whowas the PF) incorrectly deduced the location of the FAF to be 10 DME from the localizer, rather than 5 DME.He therefore prematurely descended to 500 feet MSL, 5 miles prior to the FAF and consequently hit the ground(meteorological information was: ceiling, 500 feet overcast; visibility 1.5 miles with fog). The first officer(who was new on the aircraft) did not notice, or did not make the captain aware of, the departure from theapproach procedure. The Safety Board, however, “believes it is more likely that the first officer was notmonitoring the approach closely because he was preoccupied with his other duties.”In addition to the regular tasks of the PNF, the first officer had two other tasks to perform: (1)reconfiguring the engine bleeds to aid in avoiding foreign object damage, and (2) starting the APU. Themanufacturer of the aircraft (Boeing), recommends that the bleeds be reconfigured below 10,000 feet; theMarkAir written procedure specifies doing this below 5,000 feet; a MarkAir management pilot stated“we try to keep them reconfigured as low as possible...usually down around couple thousand feet...” (p.9); the captain briefed the first officer to reconfigure the bleeds “when we roll in on final...” (p. 59).44