Take Off Alternates?

[nnc0]

Does anybody know if there is there a legal requirement or some kind of ICAO guidance for designating under what circumstances take off alternates are required.

example - Eng fail after rotation at MTOW but not enough power remaining to meet landing WAT limit at departure.

[Dr Eckener]

If you cannot return to your original airport of departure for any reason, including weather, weight, opening hours, then you need a take-off alternate. This has to be within 1 hours flight time, still air, with one engine inoperative (assuming 2 engined machine). No need for enhanced minima, it just has to satisfy the published minima for the chosen alternate.

Hope this helps.

[CR2]

Land immediately (overweight) and let the engineers sort it out afterwards? No biggie on 747F (both -2/-4).

[Intruder]

In the US, FAR 121.617:
§ 121.617 Alternate airport for departure.
(a) If the weather conditions at the airport of takeoff are below the landing minimums in the certificate holder's operations specifications for that airport, no person may dispatch or release an aircraft from
that airport unless the dispatch or flight release specifies an alternate airport located within the following distances from the airport of takeoff:
(1) Aircraft having two engines. Not more than one hour from the departure airport at normal cruising speed in still air with one engine inoperative.
(2) Aircraft having three or more engines. Not more than two hours from the departure airport at normal cruising speed in still air with one engine inoperative.
(b) For the purpose of paragraph (a) of this section, the alternate airport weather conditions must meet the requirements of the certificate holder's operations specifications.
(c) No person may dispatch or release an aircraft from an airport unless he lists each required alternate airport in the dispatch or flight release.

[Wizofoz]

Under JAR it further states that the takeoff conditions must be such that a landing can be made in the event of a single forseeable failure. Thus if your aircraft is downgraded in the event of a failure (e.g a 737 is CatI after an engine failure) the takeoff conditions must be above THAT minima, or else a take-off alternate is required.

[Denti]

Which makes the fail operational option so appealing, no take-off alternate needed in most cases as you are still CAT IIIa capable with one engine.

[fade to grey]

Don't know what you fly denti, but we cannot plan to return on one engine cat3a !

Must have a cat1 or better alternate

[Denti]

737 NGs, albeit fail operational ones. Fail operational can do CAT IIIa on one engine, so we do not need to plan a take off alternate if performance limits (GA max weights for flaps 30) are observed.

Well, currently a mix of "normal" (CAT IIIa only) and fail operational ones, but we will replace around 26 with the newer ones within the next 15 months.

[Wizofoz]

I wasn't aware that the fail-operative 737s were CatIIIa on one donk, though it makes sense. That being the case, Denti is right that you wouldn't need a take-off alternate provided the departure airport was above CatIIIa minima.

The 777 is CatIIIb on one engine, and as such we don't require a take-off alternate unless conditions are below the best approach available, up to and including 75m viz (in which case we couldn't take off anyway!!)

Interestingly, we also have the stipulation that the take-off alternate aerodrome can be 2 hours away (except in the US), provided we are in an "ETOPS Aircraft", which is interpereted as meaning an aircraft certified for ETOPS, even if we are not planned and signed out for an ETOPs sector.

[Capt. Inop]

I wasn't aware that the fail-operative 737s were CatIIIa on one donk,

They are post february 2003 due to some new hardware (autopilot).
And with the rudder channel activated providing rollout guidance CatIIIb.

Customer option (the rudder channel)

[galahad]

Takeoff alternate aerodrome is required when return for landing cannot be
made after takeoff if the weather at takeoff is below the landing minima
as in ICAO, Annex 6.
According to your example, there's airworthiness requirement that the aircraft
must have fuel jettison system if the aircraft cannot reach approach/landing
climb requirement at weight after takeoff for 15 minutes.

[mupepe]

EMB145 is single engine capable CATIII, DH 50ft.:cool: