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

Guideline #17: Procedure designers should always bear in mind the contribution which anyprocedure makes to total workload of the crew at any given time. They should be especiallysensitive to procedures that may require crew attention in times of high workload, and shouldstrive to “manage” workload by moving tasks that are not time-critical to periods of lowworkload.7.3 DECOUPLING OF TASKSTight coupling is a mechanical term which is used here to denote a phase, or a task, that is made up ofseveral actions that are interrelated, performed simultaneously, and are time dependent. The problemwith tight coupling is that when unexpected events occur, the time dependency and the interrelationbetween components make it difficult for pilots to intervene quickly and efficiently in order to contain theunexpected situation. A takeoff is an example of a tightly coupled task. Complexity and tight couplingare inherent characteristics in dynamic systems such as driving or flying. The designer's challenge is todesign the sequence of tasks in a way that tight coupling is minimized, or more realistically, managed.We are suggesting here the term decoupling. We use this term to denote the process in which thedesigner is trying to “break away” some of the tight coupling inherent in a phase or a task. In decouplingan activity the level of criticality is an important factor. Not all cockpit tasks conducted during the samephase of flight are equivalent in terms of criticality. Some may be more critical (e.g., monitoring thefinal approach), some may be less (e.g., cabin announcements).In most cases, the primary tasks are continuous (taxiing the aircraft, looking for taxiway, etc.), while thesecondary tasks are discrete tasks (entry of manifest changes into CDU, calling company to report pushbacktime, configuring bleeds). Critical primary objectives should be well “guarded.” This can be doneby decoupling secondary or tertiary tasks that may interfere with performing the primary task. Forexample, if it is decided that the primary objectives of the PNF from the FAF to touch down is to backupthe PF, then secondary tasks, such as configuration of bleeds, should be decoupled. Another exampleof procedures that decouple the primary task from the rest is the following altitude change procedure:“both pilots should refrain [italics added] from other duties during the last 1,000 feet of climb anddescent to an assigned altitude.” Finally, a classical case of decoupling of a task is the stabilizedapproach maneuver. This maneuver requires that the aircraft be configured for landing, descending onglide-slope, tracking the localizer at a appropriate speed during the last 1000 feet of the approach 17 .Guideline #18: The designer of flight-deck documentation should search for situations whereprocedures are tightly coupled, and exploit the opportunity to decouple them.7.3.1 Methods for DecouplingThe following is a list of several methods to achieve decoupling. This list is certainly not exhaustive.1. Reassigning the secondary tasks to a different phase. Some carriers opt to perform a takeoffchecklist while on the active runway. Some airlines, attempting to decouple this checklist taskfrom the more critical takeoff duties (e.g., listening to ATC, looking for traffic, mentalpreparation for takeoff, etc.), have mandated that the takeoff checklist will be conducted prior toentry into the active runway.2. Reassigning the task to another crew member. Some airlines require the flight crew to makea PA call to the passengers before taking off. Others have elected to reassign this task to thesenior flight attendant. Likewise, some airlines are considering installing an ACARS controldisplay unit in the cabin to allow the flight attendants to interact with company regardingpassenger comfort items (requesting wheel chairs, information about connecting flights, etc.).3. Minimizing the time and resources to perform an SOP. Secondary SOP's can be shortenedor relaxed, thereby freeing resources. For example, one airline which operates only two-pilotaircraft, allows the PNF to perform the AFTER TAKEOFF checklist without a formal challenge-17 The details of this procedure vary among airlines -- the concept does not.47