PDA

View Full Version : Standard Takeoff Minimum?


kuobin
12th Apr 2006, 16:04
Hell All:
I am interested in "Standard Takeoff Minimum",Any ony can tall me why two engs aircraft is required to have higher Takeoff Minimum than three or four engs aircraft?for example 2=eng aircraft req 1 mile(or RVR1500 meters)while 3 or 4 eng aircraft req only 1/2 mile (or RVR 750 meters).:ooh: thanks.

oldebloke
13th Apr 2006, 22:30
In Canada the Standard Takeoff 'VIS' is 1/2 mile..
Most Carriers have 'operational Specifications'(Due to training)of Takeoff visabilities of 1200'(or 600' depending on the runway facilities-centre line lighting etc)..The main difference between 2/engine aircraft and 3/4 engine types is that the Takeoff diversion Alternate Airport is 'closer'(one hour engine out cruise)..This in itself is only a Carrier'requirement,and these days this requirement is questionable with the Engine out Category3 capabilities of the fleets....EG:should the field requirements(lighting etc)operate one could return with an engineout autoland....:ok:

arba
14th Apr 2006, 03:38
In my SOP,

Category C a/c :
RVR 250m No center line guidance
RVR 200m with center line guidance
RVR 200m (beginning RW) additional RVR 175 with lighted center line
additional requirements :
- there must be suitable airport within one hour flght with one eng. inop. ( 2 eng. a/c)
- CAT I weather or better ( precision app. available)
- if non precision app. to be used, visibility must be 400m better than approach syst. minima to be use

FlightDetent
14th Apr 2006, 10:53
JAR OPS - 400 m standard. Anything below (down to 125 m or maybe less) is Low Visibility Take Off requiring special procedures and training. Although many crews are trained to the LVTO standard anyway and their manual may be written so that you cannot see a real difference between normal na LV take-off.

FD (the un-real)

411A
14th Apr 2006, 16:18
Now just imagine, the original question was what is the STANDARD minima.

And now, after much pontificating about the LOW it can be, the answer has been provided...400 metres.

Been this way for quite a long time, I believe.
I can remember it printed on the back of the Jeppesen chart for most European airports, for ages.

Congrats, FD, you are apparently the only one who actually RTFQ.:}

punkalouver
14th Apr 2006, 21:55
Are you sure?

The FQ asks why takeoff minimums(in the U.S. I assume as it is shown on those charts)are different for aircraft with different numbers of engines. Have wondered that for a long time. Anybody know?

411A
14th Apr 2006, 22:46
Yes, the reason is quite simple, and indeed was mentioned by someone before.
Twins have a different takeoff diversion distance/time than 3/4 engine aircraft.
Been this way for all the years I can remember.
As twins might have to return to the departure airport, whereas three/four engined types can have/do have greater flexibility in this regard, it stands to reason that they have slightly higher takeoff minima.

kuobin
16th Apr 2006, 04:59
Thanks,411A,I got your point.:O

Pilot Pete
16th Apr 2006, 12:59
Yes, the reason is quite simple, and indeed was mentioned by someone before.
Twins have a different takeoff diversion distance/time than 3/4 engine aircraft.
Been this way for all the years I can remember.
As twins might have to return to the departure airport, whereas three/four engined types can have/do have greater flexibility in this regard, it stands to reason that they have slightly higher takeoff minima.

Sorry don't get you there. Isn't it to do with controllability on the ground in the event of a high speed engine failure and associated yaw? I don't see what the time/ distance to T/O alternate has to do with minima for T/O. Twins may not HAVE TO return to departure airfiled, hence the T/O alternate if landing minima is below T/O minima (bearing in mind the capabilities of autoland on one engine in a twin). I would have thought an engine failure on a 747 would lead to less yaw than on a 767, hence it would be easier to control with regards to runway centreline, hence it could operate to lower minima.

Anyone?

PP

411A
16th Apr 2006, 15:52
You could be right, Pete, however I believe these minima were in existance well before the large widebody twins were a gleam on the designers board.
And as for controllability issues, the much older 4 engine Boeing design (speaking 707), were a real handful with an outboard engine failure approaching rotation.
I suspect the large twins today are much more benign.