NTSB Airplane Accident Reports: Crash During Approach to Landing - Flight Crew Monitoring and Workload Management

Company procedures for approach and landing in icing conditions stated that, when reconfiguring for approach and landing (extending landing gear and selecting full
flaps), pilots should activate the deice boot system when any ice accumulation, regardless of thickness, is visible on the wing leading edges and continue to monitor the leading edges for any reaccumulation. Although the CVR recorded the first officer mention to the captain that they might want to activate the deice boots at 0912:37, there is no evidence that the deice system was activated during the approach. Therefore, the Safety Board concludes that the flight crew did not activate the deice boots when configuring for the approach and landing, which was contrary to company procedures and manufacturer guidance.

The airplane performance calculations showed that, immediately after passing through about 6,100 feet, the airplane entered a large roll to the left concurrent with a sudden decrease in pitch, indicating the start of the loss of control and aerodynamic stall. No evidence exists indicating that the stall warning activated before or concurrent with the upset. In accordance with the Cessna Model 560 Citation V AFM and the design of the stall warning system, the accident airplane’s stall warning should have activated about 86 knots.

Although it could not be determined at precisely what airspeed the loss of control occurred, airplane performance calculations indicated that the stall occurred at an airspeed of about 90 knots, which was well above the expected stall speed in icing conditions of 81 knots. According to company and manufacturer guidance on approach airspeeds in icing conditions, the airplane’s airspeed at the time of the upset should have been about 114 knots.55 The performance calculations and EGPWS ground speed data showed that the airspeed continued to decrease until the loss of control. The Safety Board concludes that the flight crew failed to maintain adequate airspeed during the final approach in icing conditions, which led to an aerodynamic stall from which they did not recover.

55 According to the guidance, the approach airspeed should be Vref+10 knots, in this case, 106 knots. Because the guidance requires that 8 knots be added to the approach airspeed in icing conditions, the approach airspeed should have been 114 knots.

The Safety Board concludes that pilots could benefit from the reinforcement during training of the Cessna 560 AFM requirements to increase the airspeed and operate the deice boots during approaches when ice is present on the wings. Therefore, the Safety Board believes that the FAA should require that operational training in the Cessna 560 airplane emphasize the AFM requirements that pilots increase the airspeed and operate the deice boots during approaches when ice is present on the wings.

2.2.4 Flight Crew Monitoring and Workload Management
The Safety Board examined the flight crew’s actions during the approach to determine the role of the timing of the approach briefing in the accident sequence.
Although the flight crew had expected to land on runway 8L, based on the current ATIS information, at 0905:56, approach control issued vectors for the ILS to runway 26R. According to the CVR, the flight crew noted the change in the runway assignment and immediately tuned the radios and set the inbound course. However, subsequent discussion about the details of the runway 26R approach was not initiated until almost 5 minutes later, at 0910:47. During the remaining 2 minutes before the stall, the flight crew needed to intercept the localizer and glideslope and configure and slow the airplane for the approach. However, CVR evidence showed that, although these airplane-handling tasks were being performed, the flight crew was concurrently briefing the ILS 26R approach. Specifically, from 0912:17 to 0912:31, as the airspeed was decreasing, the flight crew briefed the missed approach procedure for runway 26R. It was only at the end of this discussion that the first officer recognized and called for the need to run the deice boots and indicated that the airplane had slowed to Vref.

The Safety Board recognizes that a runway change can disrupt a flight crew’s planning and may affect the pilots’ ability to conduct an approach briefing during a
relatively low workload phase of flight, such as the top of the descent. When the runway change occurs late in the approach, it is important for flight crews to determine how and when to conduct the briefing to ensure that the objectives of the briefing are achieved without compromising safety of flight.56 For the accident flight crew, the runway change occurred early enough for the briefing to have been completed before the pilots began to configure and slow the airplane for final approach. Literature on monitoring emphasizes The Safety Board has long recognized the importance of flight crew monitoring skills in accident prevention. For example, the Board’s 1994 safety study of 37 major flight crew-involved accidents found that, for 31 of these accidents, inadequate monitoring and/or cross-checking had occurred.57 The study found that flight crewmembers frequently failed to recognize and effectively draw attention to critical cues that led to the accident sequence. As a result of this safety study, the Board issued Safety Recommendations A-94-3 and -4 to the FAA concerning the need for enhanced training of pilot monitoring skills. The recommendations stated, in part, that the FAA should require airlines operating under 14 CFR Part 121 to provide line operational simulation training that "allows flightcrews to practice, under realistic conditions, non-flying pilot functions, including monitoring and challenging errors made by other crewmembers" and that airlines’ initial operating experience programs should include training and experience for check airmen and pilots "in enhancing the monitoring and challenging functions."58

In response to these recommendations, the FAA upgraded its written guidance to industry to enhance pilot training on monitoring. Specifically, on September 8, 1995, the FAA revised AC 120-51, "Crew Resource Management Training," to emphasize monitoring issues. The guidance in AC 120-51 stated that "effective monitoring and cross-checking can be the last line of defense that prevents an accident" and that "the

56 Industry guidance states that crews should ask ATC for assistance, such as requesting to receive delayed vectors or enter a holding pattern, when they become rushed or otherwise behind on their duties as a result of unanticipated routings.

57 For additional information, see National Transportation Safety Board, A Review of Flightcrew-Involved, Major Accidents of U.S. Carriers, 1978 through 1990, Safety Study NTSB/SS-94/01 (Washington, DC: NTSB, 1994).

58 The complete text of Safety Recommendation A-94-3 to the FAA was as follows: "Require U.S. air carriers operating under 14 CFR Part 121 to provide, for flight crews not covered by the Advanced Qualification Program, line operational simulation training during each initial or upgrade qualification into the flight engineer, first officer, and captain position that (1) allows flight crews to practice, under realistic conditions, non-flying pilot functions, including monitoring and challenging errors made by other crewmembers; (2) attunes flight crews to the hazards of tactical decision errors that are errors of omission, especially when those errors are not challenged; and (3) includes practice in monitoring and challenging errors during taxi operations, specifically with respect to minimizing procedural errors involving
inadequately performed checklists." The complete text of Safety Recommendation A-94-4 to the FAA was as follows: "Require that U.S. air carriers operating under 14 CFR Part 121 structure their initial operating experience programs to include: (a) training for check airmen in enhancing the monitoring and challenging functions of captains and first officers; (b) sufficient experience for new first officers in performing the non-flying pilot role to establish a positive attitude toward monitoring and challenging errors made by the flying pilot; and (c) experience (during initial operating experience and annual line checks) for captains in giving and receiving challenges or errors." On January 19, 1996, the Safety Board classified these recommendations "Closed—Acceptable Alternate Action" in response to the FAA’s upgrades of its training guidance.

The Safety Board is aware of recent accidents in which inadequate pilot monitoring was a causal or contributing factor to the accident and in which pilots on
approach to landing failed to observe critical and salient cues.59 These accidents demonstrate the importance of monitoring skills and effective workload management in ensuring safety of flight. Existing FAA guidance to operators addresses these skills but providing specific pilot training on effective monitoring and cockpit workload management would be a way for the aviation industry to effectively deliver and reinforce the importance of these skills to pilots. The Safety Board concludes that all operators would benefit from an increased focus on providing monitoring skills in their training programs, including those operating under 14 CFR Parts 121 and 135, as would pilots completing FAA-approved training programs for Part 91 operations.60 Therefore, the Safety Board believes that the FAA should require pilot training programs be modified to contain modules that teach and emphasize monitoring skills and workload management and include opportunities to practice and demonstrate proficiency in these areas.

2.3 Deice Boot Systems
Company and manufacturer guidance states that the surface deice boots should be used when ice buildup is estimated to be between 1/4- to 1/2-inch thick and that "early activation of the boots may result in ice bridging on the wing." During the Comair

59 For additional information, see National Transportation Safety Board, Collision With Trees on Final Approach, Federal Express Flight 1478, Boeing 727-232, N497FE, Tallahassee, Florida, July 26, 2002, Aviation Accident Report NTSB/AAR-04/02 (Washington, DC: NTSB, 2004); National Transportation Safety Board, Crash During Approach to Landing, Air Tahoma, Inc., Flight 185, Convair 580, N586P, Covington, Kentucky, August 13, 2004, Aviation Accident Report NTSB/AAR-06/03 (Washington, DC: NTSB, 2006); and National Transportation Safety Board, Crash During Approach to Landing, Business Jet Services Ltd., Gulfstream G-1159A (G-III), N85VT, Houston, Texas, November 22, 2004, Aviation Accident Brief NTSB/AAB-06/06 (Washington, DC: NTSB, 2006).

60 The Safety Board recognizes that many pilots engaged primarily in noncommercial flying under 14 CFR Part 91 do not complete formal training programs but believes that these pilots can benefit from the increased industry emphasis and specific training principles on monitoring.

However, AC 25.1419-1A states that, although ice may not be completely shed by one cycle of the boots, the residual ice will usually be removed by subsequent cycles and does not act as a foundation for a bridge of ice to form. Further, information gathered at a 1997 Airplane Deice Boot Bridging Workshop, subsequent icing tunnel tests, and flight tests conducted as part of the Comair investigation revealed that ice bridging did not occur on modern airplanes, which are equipped with deice boots that quickly inflate and deflate. The icing tunnel tests also revealed that thin (1/4 inch or less), rough ice accumulations on the wing leading edge deice boot surfaces could be, depending on distribution, as aerodynamically detrimental to an airplane’s performance as larger ice accumulations.

A search of the Safety Board accident database revealed no accidents related to ice bridging. Conversely, the Board has investigated many icing accidents in which the airplane stalled prematurely and the stall warning system did not activate before the stall because of ice accumulation on the wing leading edges. This accident, previous accident investigations, Safety Board accident data, and existing icing information clearly show that delaying the activation of the deice boots can create unsafe operations. The Safety Board concludes that ice bridging does not occur on modern airplanes; therefore, it is not a reason for pilots to delay activation of the deice boots.

As a result of its findings during the Comair flight 3272 investigation, the Safety Board issued Safety Recommendation A-98-91, which recommended that the FAA do the following:

Require manufacturers and operators of modern turbopropeller-driven airplanes in which ice bridging is not a concern to review and revise the guidance contained in
their manuals and training programs to emphasize that leading edge deicing boots should be activated as soon as the airplane enters icing conditions.

In May 2002, the FAA issued an icing test report that recommended an "early and often" approach to deice boot usage to limit the size of residual and intercycle ice
accretions. Further, in January 2003, an ARAC IPHWG recommended revisions to Parts 25 and 121 to require that deice systems be activated as soon as an airplane enters icing conditions. However, since that time, the FAA has taken no action to issue a final rule adopting the regulatory changes proposed by the ARAC IPHWG.

Although the accident airplane most likely accumulated less than 1/4-inch-thick ice while operating in the lower cloud layer, the pilots’ failure to activate the deice boots during the approach led to the continued accumulation of thin, rough ice on the protected surfaces, which can severely degrade an airplane’s performance. The circumstances of this accident, information gathered during the Comair flight 3272 accident, and reports issued by the FAA and the ARAC IPHWG clearly demonstrate that existing guidance instructing pilots to delay activation of the deice boots until they observe 1/4- to 1/2-inch-thick ice accumulation is not adequate because it does not protect against the detrimental effects caused by thin, rough ice accumulation on or aft of the protected surfaces. If pilots continue to adhere to guidance about delaying deice boot activation, similar accidents could still occur. The Safety Board concludes that activating the deice boots as soon as an airplane
enters icing conditions provides the greatest safety measure. On the basis of this accident and the Board’s continued concerns in this area, the Board believes that the FAA should require manufacturers and operators of pneumatic deice boot-equipped airplanes to revise the guidance contained in their manuals and training programs to emphasize that leading edge deice boots should be activated as soon as the airplane enters icing conditions. The new recommendation will supersede Safety Recommendation A-98-91 and will be classified "Open—Unacceptable Response."

The Safety Board is concerned that workload increases significantly when pilots of airplanes equipped with deice boots that do not cycle automatically operate in icing conditions because they must continuously monitor the ice accumulation on the airplane’s surfaces and determine when to reactivate the deice boots. This consideration is consistent with FAA concerns in AC 23.1419-2C.61 Having to operate the deice boot system manually is even more critical during the approach and landing phases of flight when pilot workload and monitoring demands are greatest.

The Safety Board concludes that manual operation of the deice boot system increases pilot workload, which can result in distraction during critical phases of flight, such as approach and landing. Therefore, the Safety Board believes that the FAA should require that all pneumatic deice boot-equipped airplanes certified to fly in known icing conditions have a mode incorporated in the deice boot system that will automatically continue to cycle the deice boots once the system has been activated.

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