Sterile Cockpit Rule

The Sterile Cockpit Rule is an FAA regulation requiring pilots to refrain from non-essential activities during critical phases of flight, normally below 10,000 feet (3048 meters). The FAA imposed the rule in 1981 after reviewing a series of accidents that were caused by flight crews who were distracted from their flying duties by engaging in non-essential conversations and activities during critical parts of the flight. One such notable accident was Eastern Air Lines Flight 212, which crashed just short of the runway at Charlotte/Douglas International Airport in 1974 while conducting an instrument approach in dense fog. The National Transportation Safety Board (NTSB) concluded that a probable cause of the accident was distraction due to idle chatter among the flight crew during the approach phase of the flight. Similar is the case of Colgan Air Flight 3407 in 2009.

In the early days of aviation, pilots had little chance to contemplate non-essential activities. Flying demanded constant attention, and the wind and engine noise in a slipstream-blasted open cockpit all but drowned out normal conversations. In the early years of instrument flying, the effort involved in "flying the beam" (navigating a course determined by the intersection of ground based radio signals by straining to listen through a headset to a scratchy audio stream of "dits and dahs") also forced pilots to concentrate on flying duties during instrument meteorological conditions. However, as aviation technology matured into the Jet Age in the 1960s, comfort and sound levels gradually became more office-like and hence more conducive to distractions. Multi-person flight and cabin crews, autopilots, in-flight meals, newspaper service and other comforts further increased the availability and convenience of non-flight related activities for flight crews during flight time. The introduction of the Cockpit Voice Recorder as an objective onboard observer played an important role in the assessment of the problem during accident investigation by the NTSB, and eventual implementation of the rules by the FAA.

...
Wikipedia