Take-off Alternate

[N1 Limit]

With regards to Take-off alternate,it's said that the requirements for landing minima for a take-off alternate are:

The weather must be above landing minima for the aerodrome at departure time.

My question is:what are these minimas?are they the same the destination whereby in the case of a Cat 2 approach we use Cat 1 minima?or the weather just has to be greater than the minimums written on the plates?Any info is appreciated

[hetfield]

The point is landing minima versus alternate minima.

So if your SOP allows to land with OEI @ CATII, it`s CATII.

[oldebloke]

The requirement for a Takeoff alternate has become a 'little' Passe at the moment.Originally it was required if low weather precluded a return..
Nowadays ,with the use of Cat3OEI,one would be hard pressed to explain to the chief Pilot why one went to the said Alt'.The only explanation would be that'operationally'the airport didn't meet Cat3 requirements at the time of return.The old Pax Heart attack simulator exercise,just after TakeOff..:sad:

[N1 Limit]

Thanx guys,but in the case of a scenario where CAT 3 doesn't exist,what would be the requirements for a Take-off alternate weather wise?

[Mansfield]

All you really need to determine is the lowest minima which you can use to return for a landing with one engine inoperative. Starting with the CAT III case:

If the airport has an available CAT III runway, with all of its equipment functioning, and your airplane is certificated for a CAT III autolanding with one engine inoperative, and your operating specifications or manuals allow this, and you and the crew are certified for such...then no takeoff alternate is required.

But, if any of those conditions cannot be met...such as, the airplane is certificated for CAT III OEI but today it has a deferred item that precludes CAT III ops, or the runway is certified, the approach plate says CAT III, but there is a NOTAM downgrading the localizer transmitter...then you need a takeoff alternate.

If your airplane is only certificated for a CAT I landing with one engine inoperative, or if the runway is only certified for CAT I operations, then that's the weather you need to avoid a takeoff alternate. Or, if your airplane is certificated for a CAT III but your company policy doesn't allow this, or the runway is downgraded, etc., etc. This can get tricky with some airplanes. The B757/767 fleet are almost universally certificated for an autolanding with one engine inoperative as long as the engine fails following selection of landing flaps. This is good to know but it doesn't count for planning purpose; these aircraft are limited to CAT I (or CAT II if manual landings are permitted) for the one engine inoperative planning requirement (such as a takeoff alternate). Only some 757/767 aircraft are certificated for an autolanding if the engine fails en route, and these aircraft, all else allowing, could plan for a CAT III autolanding with one engine inop.

At the end of the day, just figure out what the lowest minima is for a one engine inoperative approach, at that airport, that runway, with those NOTAMs and that MEL. If you have it, you're good. If not, tack on the alternate. There is probably no less expensive operational change to make...it's not as if you have to add fuel!

[alatriste]

The planning minima for after take off alternate is just the minimum required in the aproach plate expected, no additions like consider for destination alternates.
If expected aproach at take off alternate is an ILS only RVR is considered, if NPA is expected RVR and ceiling must be check.

[shortfuel]

As said above, here is some more precise reference:

Planning minima for a take-off alternate aerodrome. An operator shall only select an aerodrome as a take-off alternate aerodrome when the appropriate weather reports or forecasts or any combination thereof indicate that, during a period commencing one hour before and ending one hour after the estimated time of arrival at the aerodrome, the weather conditions will be at or above the applicable landing minima specified in accordance with OPS 1.225. The ceiling must be taken into account when the only approaches available are non-precision and/or circling approaches. Any limitation related to one-engine-inoperative operations must be taken into account.

Having said that, some CAT II/III airlines restrict take-off alternate WX to be above CAT I even if it has CAT II/III RWY.

[Denti]

You might have to take performance issues into consideration. For example the 737 is only certified for CAT III single engine for certain weights to still achieve a positive go-around climb gradient with normal CAT III OEI flap settings (30/15GA), basicly it is impossible to use that feature with the -800 both in normal and SFP version, but on the -700 it is very much available.

[PappyJ]

Originally it was required if low weather precluded a return..

It means something different now??? :confused:

[oldebloke]

The alternate had to have required WX limits within 320nm,or I hour...:E