Takeoff Configuration Warning Systems (TOCWS)
A Takeoff Configuration Warning System (TOWS) is a crucial safety feature designed to prevent aircraft from taking off when they are not in a safe configuration. This system is particularly important as it acts as a backup to the standard checklist, especially during unusual situations where the checklist might be interrupted or takeoff is delayed.
Since the late 1970s, regulations have mandated that all jet aircraft and non-jet aircraft weighing over 6,000 pounds (2,725 kg) must be equipped with a TOWS, unless they can prove that their lift or trim devices will not compromise safety. The warning system ensures pilots receive an audible alert during the initial phase of takeoff if the aircraft is not configured correctly for a safe ascent.
An unsafe takeoff configuration might mean the aircraft cannot rotate or risks stalling right after rotation. The TOWS must function correctly at all authorized power settings and under varying weights, altitudes, and temperatures. The warning continues until either the configuration is adjusted for a safe takeoff or the pilot decides to abort the takeoff roll.
The specific systems monitored by the TOWS can differ based on the aircraft type but typically include:
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Position of High Lift Devices: such as flaps and slats.
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Elevator Trim Position: or trimable horizontal stabilizer position.
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Ground Spoilers or Speedbrakes: status.
Some advanced aircraft may also monitor additional systems like rudder trim, aileron trim, parking brake engagement, and mismatched configurations between the aircraft and Flight Management System entries.
Activation of the TOWS usually occurs through conditions met by thrust lever positions or engine parameters. Once armed, sensors relay information about the monitored systems to the TOWS, triggering an alarm if a component is not in the correct takeoff configuration.
Notable Incidents Involving Improper Takeoff Configurations
Several accidents highlight the importance of proper takeoff configurations:
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F50, Helsinki, Finland (2021): An engine malfunction caused uncommanded propeller feathering during takeoff, leading to an emergency landing.
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B77L, Paris CDG, France (2015): A crew error resulted in a reduced thrust setting, leading to a tailstrike as the aircraft attempted to take off.
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DC10, Macau SAR, China (2005): Incorrect flap settings led to a dangerously extended takeoff roll, resulting in damage upon ascent.
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A140, Tehran Mehrabad, Iran (2014): An engine failure occurred post-V1, causing the aircraft to stall and crash due to improper flap settings.
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A333, Chicago O’Hare, IL, USA (2013): An A330 sustained significant damage from a tail strike, which went unnoticed until after landing.
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B733, Montpelier, France (2011): Unexpected slat deployment during takeoff led to a near-stall situation.
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B732, Medan, Indonesia (2005): A failed takeoff resulted in a catastrophic crash, killing many on board and on the ground.
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MD83, Lanzarote, Spain (2007): The aircraft experienced violent roll oscillations after takeoff due to incorrect flap settings.
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MD82, Madrid Barajas, Spain (2008): The aircraft crashed after takeoff due to flaps and slats being retracted.
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MD82, Detroit, MI, USA (1987): A takeoff attempt ended in disaster due to failure to become airborne, resulting in numerous fatalities.
These incidents underline the vital role that Takeoff Configuration Warning Systems play in aviation safety.
