Isso não é específico para ETOPS, mas está relacionado a terrenos altos. Quando sobrevoar um terreno que limita sua capacidade de chegar ao seu destino ou destino alternativo, você planeja alternativos adicionais chamados alternativos "drift-down". O plano de vôo é então segmentado em segmentos de desvio que determinam em qual alternativo você vai pousar se necessário para esse segmento de vôo.
A informação de desvio será parte da liberação de despacho e garante que, a partir de qualquer ponto em sua rota com uma falha de motor, você pode atender aos requisitos de liberação de obstáculos enquanto desce em direção a um aeroporto alternativo adequado.
As rotas que eu voava entre os EUA e o México geralmente tinham alternativas alternadas, já que havia áreas em muitas de nossas rotas que não podíamos retornar a nosso aeroporto de partida ou fazer nosso destino se tivéssemos uma falha de motor. Nesses casos, referenciamos o segmento em que estávamos e seguimos para o substituto desse segmento.
A base regulatória para os procedimentos e alternativas de deriva é 14 CFR 121.191 . A sinopse é que o vôo com um motor com falha deve ser capaz de avançar para um destino ou alternar a partir de qualquer ponto ao longo da rota, mantendo os requisitos específicos de liberação do terreno. Os suplentes "drift-down" devem atender aos mesmos requisitos que os suplentes normais (clima, adequação) e devem estar presentes na liberação de despacho.
Combinando isso com o ETOPS, os substitutos de drift teriam que estar dentro da faixa de ETOPS, além dos requisitos de desvio de terreno.
O regs:
§121.191 Airplanes: Turbine engine powered: En route limitations: One engine inoperative.
(a) No person operating a turbine engine powered airplane may take off that airplane at a weight, allowing for normal consumption of fuel and oil, that is greater than that which (under the approved, one engine inoperative, en route net flight path data in the Airplane Flight Manual for that airplane) will allow compliance with paragraph (a) (1) or (2) of this section, based on the ambient temperatures expected en route:
(1) There is a positive slope at an altitude of at least 1,000 feet above all terrain and obstructions within five statute miles on each side of the intended track, and, in addition, if that airplane was certificated after August 29, 1959 (SR 422B) there is a positive slope at 1,500 feet above the airport where the airplane is assumed to land after an engine fails.
(2) The net flight path allows the airplane to continue flight from the cruising altitude to an airport where a landing can be made under §121.197, clearing all terrain and obstructions within five statute miles of the intended track by at least 2,000 feet vertically and with a positive slope at 1,000 feet above the airport where the airplane lands after an engine fails, or, if that airplane was certificated after September 30, 1958 (SR 422A, 422B), with a positive slope at 1,500 feet above the airport where the airplane lands after an engine fails.
(b) For the purposes of paragraph (a)(2) of this section, it is assumed that—
(1) The engine fails at the most critical point en route;
(2) The airplane passes over the critical obstruction, after engine failure at a point that is no closer to the obstruction than the nearest approved radio navigation fix, unless the Administrator authorizes a different procedure based on adequate operational safeguards;
(3) An approved method is used to allow for adverse winds:
(4) Fuel jettisoning will be allowed if the certificate holder shows that the crew is properly instructed, that the training program is adequate, and that all other precautions are taken to insure a safe procedure;
(5) The alternate airport is specified in the dispatch or flight release and meets the prescribed weather minimums; and
(6) The consumption of fuel and oil after engine failure is the same as the consumption that is allowed for in the approved net flight path data in the Airplane Flight Manual.