Overwing exits
Encyclopedia
Overwing exits are found on passenger aircraft to provide a means of passenger evacuation
onto the wing, where they either continue off the trailing edge
by sliding down the extended flaps or by using an evacuation slide
that deploys when the exit is opened.
Overwing exits are smaller in width and height than standard emergency exit
s on an aircraft
, and therefore have a reduced evacuation capacity, and are typically added to aircraft where there is insufficient evacuation capacity at the main doors to obtain a 90 second evacuation, but where the addition of another set of full sized exits is not necessary to accomplish this.
Overwing exits are primarily self-help exits meaning that in an emergency evacuation the passengers seated immediately adjacent to the exit will be responsible for assessing for external hazards and opening the exit.
Another hazard in the use of overwing exits is them being improperly opened (usually a result of passengers in these seats not paying attention to the verbal briefing provided pre-departure, or not observing the opening instructions on the safety card and on the exit). The majority of overwing exits involve the passenger physically removing the hatch from its frame and disposing of it outside on the wing without blocking the exit. Research conducted at the Cranfield Institute
in the UK showed that many passengers are prone to leaving the exit hatch on the seat next to the exit, thereby hindering other passengers' egress through the exit.
Additionally, during aircraft evacuations, it has been found that the majority of overwing window exit designs of Boeing
& 737 (NG) Next Generation Line along with the Airbus A320
, hamper evacuation in comparison with traditional floor level exits due, to the inherent "step up and through motion" required of passengers as they exit the aircraft, unlike the designs of older generation wide body aircraft such as the McDonnell Douglas DC-10
and Lockheed L1011 which are all floor level.
, which is not considered an overwing exit) in use on modern aircraft. The disposable hatch type exit is the most common, where the operator must first remove the hatch from its frame before disposing of it on the wing, away from the exit. The second type is the self disposing hatch, found on more modern aircraft (such as the Boeing 737 Next Generation
) and has been designed to both simplify the opening of the exit and to remove the hazard of the removed hatch blocking the exit. This is accomplished by the passengers simply pulling in and down on a handle recessed into the top of the door and initiating the exit's self-opening mechanism, whereby the door rotates up and out on a hinge at the top of the exit frame.
Depending on the height of the aircraft from the ground, an overwing exit may have an automatically inflating slide that is housed within the fuselage near to the exit(s). If the exit is opened the slide will automatically deploy and inflate to provide a means of evacuation from the wing to the ground. Only the slide on the same side of the aircraft as the open hatch will inflate. However, on aircraft where there are a pair of adjacent overwing exits on both sides of the aircraft (i.e. four in total), such as on some Boeing 767-300 variants, opening one of the pair of doors will deploy the slide. Should slide inflation fail, there is a manual inflation handle within the door frame of each exit (the location of which varies but is always indicated on the safety information card) which can be pulled to inflate the slide. Should this also fail the use of another exit should be sought.
Emergency evacuation
Emergency evacuation is the immediate and rapid movement of people away from the threat or actual occurrence of a hazard. Examples range from the small scale evacuation of a building due to a bomb threat or fire to the large scale evacuation of a district because of a flood, bombardment or...
onto the wing, where they either continue off the trailing edge
Trailing edge
The trailing edge of an aerodynamic surface such as a wing is its rear edge, where the airflow separated by the leading edge rejoins. Essential control surfaces are attached here to redirect the air flow and exert a controlling force by changing its momentum...
by sliding down the extended flaps or by using an evacuation slide
Evacuation slide
An evacuation slide is an inflatable slide used to evacuate an aircraft quickly. An escape slide is required on all commercial aircraft where the door sill height is such that, in the event of an evacuation, passengers would be unable to "step down" from the door uninjured An evacuation slide is...
that deploys when the exit is opened.
Overwing exits are smaller in width and height than standard emergency exit
Emergency exit
An emergency exit in a structure is a special exit for emergencies such as a fire: the combined use of regular and special exits allows for faster evacuation, while it also provides an alternative if the route to the regular exit is blocked by fire, etc....
s on an aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
, and therefore have a reduced evacuation capacity, and are typically added to aircraft where there is insufficient evacuation capacity at the main doors to obtain a 90 second evacuation, but where the addition of another set of full sized exits is not necessary to accomplish this.
Overwing exits are primarily self-help exits meaning that in an emergency evacuation the passengers seated immediately adjacent to the exit will be responsible for assessing for external hazards and opening the exit.
Hazards
The primary hazard involving the use of overwing exits is passengers not waiting to be given the command to evacuate, but rather initiating it themselves. While many passengers (especially frequent fliers) would believe that they are adult enough and educated enough to decide that they need to get out of an aircraft, they are not trained in the specific dangers or the sequence of events required to decide when a full-scale evacuation is needed. Also, passengers will frequently open an exit as soon as evacuation begins which may result in them evacuating into danger. This occurred in the Ryanair engine fire in Stansted Airport in 2002, where passengers evacuated themselves onto a burning wing, despite airport fire services shouting at them to return inside the aircraft and evacuate via a usable exit . Typically, these problems do not occur at floor level, full sized, exit doors because these are operated by flight attendants in an emergency who have extensive emergency training.Another hazard in the use of overwing exits is them being improperly opened (usually a result of passengers in these seats not paying attention to the verbal briefing provided pre-departure, or not observing the opening instructions on the safety card and on the exit). The majority of overwing exits involve the passenger physically removing the hatch from its frame and disposing of it outside on the wing without blocking the exit. Research conducted at the Cranfield Institute
Cranfield Institute
The Cranfield Institute for Safety, Risk and Reliability is a part of Cranfield University in the UK. It is primarily a teaching and research facility, but also offers safety-related consultancy to businesses.- Facilities :The Cranfield Institute has several simulators designed for risk and hazard...
in the UK showed that many passengers are prone to leaving the exit hatch on the seat next to the exit, thereby hindering other passengers' egress through the exit.
Additionally, during aircraft evacuations, it has been found that the majority of overwing window exit designs of Boeing
Boeing
The Boeing Company is an American multinational aerospace and defense corporation, founded in 1916 by William E. Boeing in Seattle, Washington. Boeing has expanded over the years, merging with McDonnell Douglas in 1997. Boeing Corporate headquarters has been in Chicago, Illinois since 2001...
& 737 (NG) Next Generation Line along with the Airbus A320
Airbus A320
The Airbus A320 family is a family of short- to medium-range, narrow-body, commercial passenger jet airliners manufactured by Airbus Industrie.Airbus was originally a consortium of European aerospace companies, and is now fully owned by EADS. Airbus's name has been Airbus SAS since 2001...
, hamper evacuation in comparison with traditional floor level exits due, to the inherent "step up and through motion" required of passengers as they exit the aircraft, unlike the designs of older generation wide body aircraft such as the McDonnell Douglas DC-10
McDonnell Douglas DC-10
The McDonnell Douglas DC-10 is a three-engine widebody jet airliner manufactured by McDonnell Douglas. The DC-10 has range for medium- to long-haul flights, capable of carrying a maximum 380 passengers. Its most distinguishing feature is the two turbofan engines mounted on underwing pylons and a...
and Lockheed L1011 which are all floor level.
Operation
There are principally two types of overwing exits (excluding the full-sized door on the likes of the Boeing 747Boeing 747
The Boeing 747 is a wide-body commercial airliner and cargo transport, often referred to by its original nickname, Jumbo Jet, or Queen of the Skies. It is among the world's most recognizable aircraft, and was the first wide-body ever produced...
, which is not considered an overwing exit) in use on modern aircraft. The disposable hatch type exit is the most common, where the operator must first remove the hatch from its frame before disposing of it on the wing, away from the exit. The second type is the self disposing hatch, found on more modern aircraft (such as the Boeing 737 Next Generation
Boeing 737 Next Generation
The Boeing 737 Next Generation, commonly abbreviated as Boeing 737NG, is the name given to the -600/-700/-800/-900 series of the Boeing 737 after the introduction of the -300/-400/-500 Classic series. They are short- to medium-range, narrow-body jet airliners...
) and has been designed to both simplify the opening of the exit and to remove the hazard of the removed hatch blocking the exit. This is accomplished by the passengers simply pulling in and down on a handle recessed into the top of the door and initiating the exit's self-opening mechanism, whereby the door rotates up and out on a hinge at the top of the exit frame.
Depending on the height of the aircraft from the ground, an overwing exit may have an automatically inflating slide that is housed within the fuselage near to the exit(s). If the exit is opened the slide will automatically deploy and inflate to provide a means of evacuation from the wing to the ground. Only the slide on the same side of the aircraft as the open hatch will inflate. However, on aircraft where there are a pair of adjacent overwing exits on both sides of the aircraft (i.e. four in total), such as on some Boeing 767-300 variants, opening one of the pair of doors will deploy the slide. Should slide inflation fail, there is a manual inflation handle within the door frame of each exit (the location of which varies but is always indicated on the safety information card) which can be pulled to inflate the slide. Should this also fail the use of another exit should be sought.