Em um dos comentários sobre a esta pergunta (sob a resposta aceita), alguém observa que
Aircraft can legally fly without a system to alert the crew when they are landing with gear up, etc.
Esses sistemas são instalados em aeronaves comerciais como um requisito legal?
Todas as aeronaves movidas a turbina utilizadas no serviço aéreo programado sob a CFR Parte 121 devem ter um TAWS aprovado instalado;
§121.354 Terrain awareness and warning system.
(a) Airplanes manufactured after March 29, 2002. No person may operate a turbine- powered airplane unless that airplane is equipped with an approved terrain awareness and warning system that meets the requirements for Class A equipment in Technical Standard Order (TSO)-C151. The airplane must also include an approved terrain situational awareness display.
(b) Airplanes manufactured on or before March 29, 2002. No person may operate a turbine-powered airplane after March 29, 2005, unless that airplane is equipped with an approved terrain awareness and warning system that meets the requirements for Class A equipment in Technical Standard Order (TSO)-C151. The airplane must also include an approved terrain situational awareness display.
(c) Airplane Flight Manual. The Airplane Flight Manual shall contain appropriate procedures for—
(1) The use of the terrain awareness and warning system; and
(2) Proper flight crew reaction in response to the terrain awareness and warning system audio and visual warnings.
O sistema TAWS inclui as funções do sistema de aviso de proximidade à terra (GPWS) mais antigo.
O modo GPWS 4, voa para o terreno com menos de 500 de distância do terreno dos pés e não está na configuração de pouso, fornece alertas para a tripulação ao inserir um envelope definido abaixo dos pés do 500 (com base na altura e na taxa de descida) e a engrenagem não está em pouso configuração. Há também um envelope de alerta para os Flaps que não estão na configuração de aterrissagem.
O alerta de modo 4 consiste em um alerta sonoro "MUITO BAIXO, ENGRENAGEM. MUITO BAIXO, ENGRENAGEM".
Mais básicos que o requisito TAWS são os requisitos de certificação para aeronaves da categoria transporte, especificamente o 14 CFR 25.729 (e) (2)
14 CFR 25.729 (e) Position indicator and warning device. If a retractable landing gear is used, there must be a landing gear position indicator easily visible to the pilot or to the appropriate crew members (as well as necessary devices to actuate the indicator) to indicate without ambiguity that the retractable units and their associated doors are secured in the extended (or retracted) position. The means must be designed as follows:
(1) If switches are used, they must be located and coupled to the landing gear mechanical systems in a manner that prevents an erroneous indication of “down and locked” if the landing gear is not in a fully extended position, or of “up and locked” if the landing gear is not in the fully retracted position. The switches may be located where they are operated by the actual landing gear locking latch or device.
(2) The flightcrew must be given an aural warning that functions continuously, or is periodically repeated, if a landing is attempted when the landing gear is not locked down.
(3) The warning must be given in sufficient time to allow the landing gear to be locked down or a go-around to be made.
(4) There must not be a manual shut-off means readily available to the flightcrew for the warning required by paragraph (e)(2) of this section such that it could be operated instinctively, inadvertently, or by habitual reflexive action.
(5) The system used to generate the aural warning must be designed to minimize false or inappropriate alerts.
(6) Failures of systems used to inhibit the landing gear aural warning, that would prevent the warning system from operating, must be improbable.
(7) A flightcrew alert must be provided whenever the landing gear position is not consistent with the landing gear selector lever position.
Para o 767, estes são os requisitos para acionar um aviso de configuração de pouso.
(7) Landing Configuration Warning Module Function (Fig. 8) (a) The landing configuration warning module provides aural and visual warnings for improper airplane configuration during landing. The module receives a dual input of |12 volts dc and +5 volts dc from power supply modules A and B.
(b) The landing configuration warning consists of the master WARNING light, siren aural warning, CONFIG light, and level A EICAS message.
(c) The landing configuration warning logic is enabled when the module receives the landing gear not down and locked discrete signal from the proximity switch electronics unit.
(d) When this logic is enabled and any of the following conditions occur, the landing configuration warning is provided. The outputs for each condition are as listed below:
1) The trailing edge flaps are set to 25 or 30 degrees: a) red master WARNING lights b) amber CONFIG light c) siren aural warning d) level A EICAS message
2) Both left and right thrust levers are set to idle and the radio altitude is below 800 feet: a) red master WARNING lights b) amber CONFIG light c) siren aural warning d) level A EICAS message
3) Either left or right thrust lever is set to idle, the radio altitude is below 800 feet, and the time delay as noted below has expired: a) red master WARNING lights b) amber CONFIG light c) siren aural warning d) level A EICAS message NOTE: A one time delay of 140 seconds is triggered by the edge of the landing-gear-up transition pulse. This delay allows the airplane to reach an altitude of greater than 800 feet and prevents a warning if only one engine is throttled back at takeoff or go-around. If either 140 seconds have elapsed or the airplane has exceeded 800 feet altitude, the system reverts back to providing a warning from a single engine throttle back.
4) A radio altimeter failure exists, either thrust lever is set to the idle position, and the airplane is in a clean wing configuration (flaps and slats are fully retracted): a) amber CONFIG light b) level A EICAS message
5) A radio altimeter failure exists, either thrust lever is set to the idle position, and either the flaps or slats are not fully retracted (NOT CLEAN WING): a) red master WARNING b) siren aural warning