Normally an evacuation is started by an order from the aircraft commander. Sometimes, however, passengers may start the procedure without being told to. This may happen for a variety of reasons:
Perceived danger. Passengers rarely experience emergencies so they may not assess the siutation correctly. Abnormality, combined with uncertainty, may cause them to panic and act quickly, one of the possible scenarios being to start an emergency evacuation.
Misunderstanding. In an abnormal situation, a rapid disembarkation order may be misinterpreted as an evacuation one. Also, the lack of any instructions (or information) from the flight deck may contribute to a passengers' decision to act. They realise something is wrong and there is an urge to do something.
Crew Incapacitation. If the pilots and the cabin crew are incapacitated they cannot organise an evacuation which leaves this up to the passengers.
There are several issues associated with this behaviour:
Increased risk of evacuation injuries. The passengers are usually not familiar and most have no practical training with emergency evacuations. Therefore, lack of guidance from the cabin crew may contribute to inappropriate passenger actions resulting in injuries.
Lack of coordination. Coordinated actions between the flight crew, the cabin crew and the passengers normally result in smooth flow of people out of the aircraft. When this is not the case, the process is not as efficient and precious time may be lost. For example, the crew may not extend the flaps if they are unaware that the evacuation has already started. This, in turn, may cause the people who have left the aircraft via the overwing exits to try to return inside.
Ground risks. Passengers on the movement area are generally guided so as to avoid various airport hazards. When an evacuation is done either after a commander's order or on cabin crew initiative, they are directed by the cabin crew after leaving the aircraft. If this is not the case, the passengers may put themselves at risk (by e.g. remaining too close to the aircraft). It is also possible that they stray in different directions which makes it harder to count how many have exited the aircraft (and thus determine how many are still inside).
Accidents & Incidents
The Following is a list of events where an evacuation started on passengers' initiative:
A320, en-route, east of Cork Ireland, 2017 (On 2 November 2017, the flight crew of an Airbus A320 climbing out of Cork detected a “strong and persistent” burning smell and after declaring a MAYDAY returned to Cork where confusing instructions from the crew resulted in a combination of the intended precautionary rapid disembarkation and an emergency evacuation using escape slides. The Investigation highlighted the necessity of clear and unambiguous communications with passengers which distinguish these two options and in particular noted the limitations in currently mandated pre flight briefings for passengers seated at over wing emergency exits.)
B738 / B738, Toronto Canada, 2018 (On 5 January 2018, an out of service Boeing 737-800 was pushed back at night into collision with an in-service Boeing 737-800 waiting on the taxiway for a marshaller to arrive and direct it onto the adjacent terminal gate. The first aircraft’s tail collided with the second aircraft’s right wing and a fire started. The evacuation of the second aircraft was delayed by non-availability of cabin emergency lighting. The Investigation attributed the collision to failure of the apron controller and pushback crew to follow documented procedures or take reasonable care to ensure that it was safe to begin the pushback.)
B738, Georgetown Guyana, 2011 (On 30 July 2011, a Boeing 737-800 overran the wet landing runway at Georgetown after a night non-precision approach, exited the airport perimeter and descended down an earth embankment. There were no fatalities but the aircraft sustained substantial damage and was subsequently declared a hull loss. The Investigation attributed the overrun to a touchdown almost two thirds of the way down the runway and failure to utilise the aircraft’s full deceleration capability. Loss of situational awareness and indecision as to the advisability of a go-around after a late touchdown became inevitable was also cited as contributory to the outcome.)
DH8C, Toronto Canada, 2019 (On 10 May 2019, a Bombardier DHC8-300 taxiing in at Toronto at night was hit by a fuel tanker travelling at “approximately 25 mph” which failed to give way where a designated roadway crossed a taxiway causing direct crew and indirect passenger injuries and substantial damage. The Investigation attributed the collision to the vehicle driver’s limited field of vision in the direction of the aircraft coming and lack of action to compensate for this, noting the need for more effective driver vigilance with respect to aircraft right of way rules when crossing taxiways. The aircraft was declared beyond economic repair.)
DH8D, Yangon Myanmar, 2019 (On 8 May 2019, a Bombardier DHC8-400 making its second approach to Yangon during a thunderstorm touched down over halfway along the runway after an unstabilised approach but then briefly became airborne again before descending very rapidly and sustaining extreme structural damage on impact before sliding off the end of the runway. The Investigation found that prior to the final rapid descent and impact, the Captain had placed the power levers into the beta range, an explicitly prohibited action unless an aircraft is on the ground. No cause for the accident other than the actions of the crew was identified.)