B737-800 FMC
Thread Starter
Join Date: Nov 2010
Location: Auh
Posts: 111
Likes: 0
Received 0 Likes
on
0 Posts
B737-800 FMC
Sorry got confused about the reference altitude for the speed restriction in the VNAV climb and descent pages (i.e 250/100) is it AGL or MSL? Or it only refers to the Altimeter indicator? And in this case if the transition altitude/transition level is higher than 10,000 then it's going to be MSL (i.e 250/10,000 + elevation?) and if lesser then the input should be just 250/100 (flying STD)?
Join Date: Oct 2011
Location: On earth
Posts: 121
Likes: 0
Received 0 Likes
on
0 Posts
You probably misunderstood me.I said AGL related to transition Altitude/Level.If the Transition is below FL100 it is obvious it would be FL100,if it is above, it would be 10000F,in both cases plus the Airport Elevation.Usually,you have Low Transition in airports with Low Elevation and High Transition with High Elevation.Related to that, you either go with AGL or MSL.
Join Date: May 2001
Location: A few degrees South
Posts: 809
Likes: 0
Received 0 Likes
on
0 Posts
Nothing to do with AGL or MSL.
It is just depending on what you reach first, FL100 or 10.000 ft.
Just as you would do without FMS.
Common sense, and an understanding of TA, Tl will answer your question.
It is just depending on what you reach first, FL100 or 10.000 ft.
Just as you would do without FMS.
Common sense, and an understanding of TA, Tl will answer your question.
Thread Starter
Join Date: Nov 2010
Location: Auh
Posts: 111
Likes: 0
Received 0 Likes
on
0 Posts
Related to that, you either go with AGL or MSL.
Join Date: May 2001
Location: A few degrees South
Posts: 809
Likes: 0
Received 0 Likes
on
0 Posts
No, your input will stay the same: 250/100. The FMC knows, based on the TA if it is Alt or Level. Forget Field elevation, it will be 30 miles away from your field when you reach this point anyway.
Thread Starter
Join Date: Nov 2010
Location: Auh
Posts: 111
Likes: 0
Received 0 Likes
on
0 Posts
Thanks latetonite. So even during high elevation (i.e 7000ft) with TA and TL higher than 10,000 ft my input will stay 250/100 and the VNAV will keep the speed until 17,000ft (STD)?
Join Date: May 2013
Location: London
Posts: 121
Likes: 0
Received 0 Likes
on
0 Posts
Thanks latetonite. So even during high elevation (i.e 7000ft) with TA and TL higher than 10,000 ft my input will stay 250/100 and the VNAV will keep the speed until 17,000ft (STD)?
Join Date: Mar 2001
Location: I wouldn't know.
Posts: 4,498
Likes: 0
Received 0 Likes
on
0 Posts
The speed restrictions on the descend/climb page are altitudes/flight level and therefore reference to either standard or MSL depending on your TA/TL entry. The values on the TO page 2 are heights and are in reference to aerodrome level. As far as I know TO 2 is the only page used during normal daily operation that uses heights.
Join Date: May 2001
Location: A few degrees South
Posts: 809
Likes: 0
Received 0 Likes
on
0 Posts
Einul: I see where I have misled you.
You seem to be preoccupied with 10,000' above the ground.
You do not want to fly, in your case, up to 17,000' at 250 knots.
You care about 10.000 ft QNH, or QNE on the way down.
Yes, if you would take of at 7000', you might want to restrict your 250 kts a bit longer, so a manual entry would be required.
As quoted, LVL Change would be the easiest solotion.
You seem to be preoccupied with 10,000' above the ground.
You do not want to fly, in your case, up to 17,000' at 250 knots.
You care about 10.000 ft QNH, or QNE on the way down.
Yes, if you would take of at 7000', you might want to restrict your 250 kts a bit longer, so a manual entry would be required.
As quoted, LVL Change would be the easiest solotion.
Thread Starter
Join Date: Nov 2010
Location: Auh
Posts: 111
Likes: 0
Received 0 Likes
on
0 Posts
Again and again, if FMC knows our 10,000ft MSL or FL100 (reference to our TA and TL entries) then why at 7000ft elevation our entry should be 250/170? Under what condition our entry should be 250/10,000+F.E? I was looking for a complete precise answer
Join Date: Jul 2001
Location: East of West and North of South
Posts: 549
Likes: 0
Received 0 Likes
on
0 Posts
You are asking about the speed restriction on the FMC climb and descend pages, right? If so:
240/100 is with reference to either 10.000' MSL or FL100 STD.
Which one, is decided by the:
1) Airport/departure (for climb) you have loaded in the FMC.
2) Airport/approach (descent) you have loaded in the FMC.
The TA/TL is saved in the database together with the above mentioned procedures. If you do not select a procedure (i.e. an airport with out a departure procedure), the FMC assumes TA is 18.000 feet (can be set manually though on take-off reference page 2 manually). Hence the speed restriction will be 10.000' MSL.
Under no circumstances does the 240/100 refers to AGL. That means that if your airport is at 7.000', the VNAV will keep your descent speed until reaching 10.000' MSL or 3.000' AGL before reducing to 240. Unless you manually change the entry to e.g. 240/170, should you so desire.
Hope I wrote it in a way that doesn't cause you further confusion.
240/100 is with reference to either 10.000' MSL or FL100 STD.
Which one, is decided by the:
1) Airport/departure (for climb) you have loaded in the FMC.
2) Airport/approach (descent) you have loaded in the FMC.
The TA/TL is saved in the database together with the above mentioned procedures. If you do not select a procedure (i.e. an airport with out a departure procedure), the FMC assumes TA is 18.000 feet (can be set manually though on take-off reference page 2 manually). Hence the speed restriction will be 10.000' MSL.
Under no circumstances does the 240/100 refers to AGL. That means that if your airport is at 7.000', the VNAV will keep your descent speed until reaching 10.000' MSL or 3.000' AGL before reducing to 240. Unless you manually change the entry to e.g. 240/170, should you so desire.
Hope I wrote it in a way that doesn't cause you further confusion.
