Distraction is an important aspect of human factors, having contributed to many accidents and/or incidents in the history of aviation. It can be defined as a condition generated in the operating environment that affects or complicates the performance of a task or a crews compliance with applicable standards.
There can be multiple causes of distraction of flight crew on a flight deck. These include and are not limited to:
This includes non-relevant communication taking place within the cockpit, especially during periods of high workload. This is the primary reason behind many airlines adopting a "sterile cockpit" policy below 10,000 feet, wherein the crew must refrain from any non-relevant conversation, or chit-chat, so that maximum attention can be paid to the airplane flight path. The most notable accident caused due to a distraction caused by irrelevant communication was that of Eastern Air Lines Flight 212, which crashed just short of the runway while carrying out an instrument approach into Charlotte airport in challenging weather conditions, killing 71 passengers. The investigation revealed that during the approach, flight crew engaged in non-essential conversation on topics like politics and used cars!
Flight attendant entering the flight
Cabin crew are strictly instructed in most airlines to refrain from calling or entering the flight deck during periods of high cockpit workload, unless safety dictates otherwise. Within my own organisation, there was an incident, wherein a B777 whilst in descent in Chinese airspace was instructed by the ATC to increase its descent rate to 3000 fpm. The pilot selected the "Vertical Speed Mode" for the descent. As the airplane's descent rate increased, so did its indicated airspeed. Since there is no "overspeed protection" on the B777, if descending in the VS mode, the airplane momentarily exceeded its Vmo. The pilot had been distracted from monitoring the airspeed due to the in flight purser entering the flight deck to fill out the cabin defect log and explaining the cabin defects to the pilot.
Calls from ATC or Company
Similarly, there have been and there continue to be umpteen number of cases wherein the pilots have failed to monitor critical safety aspects of the flight while they were busy communicating either with the ATC or company.
Pilots are highly trained individuals, used to performing routine tasks over and over again, on a day to day basis. Hence, they often develop good levels of expertise and skills in doing so over a period of time. However, the flip side of this is when a non-normal situation exists. Pilots tend to get distracted by the non-normal condition to such an extent that they fail to monitor their flight path. Prime examples of this are United Airlines Flight 173 and Easter Air Lines Flight 401. Both airplanes crashed while the crew turned their attention to a landing gear abnormality and thus failed to monitor their critical airplane systems and flight path.
Heads Down Activity
This includes reprogramming of on board computers and flight management systems during periods of heavy workload, which can preclude pilots from monitoring the airplanes flight path when the airplane is operating at low altitudes within a dense network of airspace.
General Consequences of Distractions
As it can be seen, distraction can seriously hamper the safety of a flight. Some of the general consequences of distraction include, and are not limited to, breaking the flow of cockpit procedures, increased workload, reduced situational awareness, fixation, missing/misinterpreting of ATC instructions, etc. Clearly, every single consequence can have a devastating impact on the safety of the flight. Some of the situations, which can arise as a consequence of distraction include, and, again, are not limited to, runway/taxiway incursion, incorrect configuration for takeoff, level busts, unstable approaches, wrong input of weights into the FMS and incorrect computation of takeoff speeds.
Most international carriers globally, incorporate a Safety Management System (SMS), which encourages reporting instances, whereby the safety of a flight was compromised. The good part of such a system is that its generally non-punitive, unless there is an intentional violation, which compromises the safety of the flight. It thus gains the confidence of the pilots and makes the system more effective. The company must make a conscious effort to expose its flight crew to the potential hazards of distractions. Strict adherence to the 'Sterile Cockpit Rule' is implemented. Cabin crew and ground staff are trained and instructed to refrain from interrupting the cockpit crew while they're in the midst of a briefing or entering critical flight data into the FMS, including computation of takeoff speeds. Strict adherence to SOP is mandated and checklist discipline is reinforced during line and simulator training. The key here is for every company to "educate" it's staff with regards to the challenge that is posed by distraction, affecting the safety of the flight.