Arming LNAV/VNAV

[jetsflier 87]

Just out of curiosity, why?

 

Usually, from what I've seen, aircraft get a few hundred feet up before they turn onto course. And I don't want to be allowing my aircraft to turn when I'm still just above the airport, that could be dangerous.

[Spin737 102]

Usually, from what I've seen, aircraft get a few hundred feet up before they turn onto course. And I don't want to be allowing my aircraft to turn when I'm still just above the airport, that could be dangerous.

Typically, you'll turn at 400' unless a SID requires otherwise. That's the standard for the US and countries that use TERPS. In some situations, you might be required to turn as early as 50'.

 

Sometimes not  turning low to the ground can be bad (eg. PAJN 26 departures).

[Copper. 78]

http://www.b737.org.uk/737_IB_2011-01.pdf

 

Some airlines with U10.8A still don't incorporate arming VNAV on the ground due to this bulletin.

 

Brian Nellis.

[Vagabondo 23]

 

 

Some airlines with U10.8A still don't incorporate arming VNAV on the ground due to this bulletin.

Well researched Brian. We still arm VNAV on during on the ground despite the bulletin. The recommendation is to consider not arming it if the conditions for windshear exist. The further point is, if windshear is anticipated, then one delays the departure :excl:

[E6BAV8R 88]

Usually, from what I've seen, aircraft get a few hundred feet up before they turn onto course. And I don't want to be allowing my aircraft to turn when I'm still just above the airport, that could be dangerous.

 

Why not just fly it straight ahead manually or use Heading Select?  None the less, if the SID calls for a turn immediately after departure than that is what you need to fly regardless. Most airliners can activate the autopilot and/or turn as low as 200'.

[Porthos 9]

 Most airliners can activate the autopilot and/or turn as low as 200'.

 

Greg not quite.

 

regarding autopilot activation

 

Airbus can mostly arm at around 50FT off the deck and for some companies that is SOP..I kid you not.

 

With the NG for example it is physically impossible to engage the autopilot below 400FT.

 

The turn is dependant upon the rules; whether it be TERPS or ICAO PANSOPS, and whether its conventional type nav or RNAV

[machine2035 176]

Airbus can mostly arm at around 50FT off the deck and for some companies that is SOP..I kid you not.

 

I feel sorry for the poor sods up at the helm who fly with airlines that dictate that.

 

 

[E6BAV8R 88]

Greg not quite.

 

regarding autopilot activation

 

Airbus can mostly arm at around 50FT off the deck and for some companies that is SOP..I kid you not.

 

With the NG for example it is physically impossible to engage the autopilot below 400FT.

 

The turn is dependant upon the rules; whether it be TERPS or ICAO PANSOPS, and whether its conventional type nav or RNAV

 

You don't need to be on a SID or Autopilot to make a turn, and it has nothing to do with TERPS requirements for which the aircraft is certified to be able to turn at a minimum altitude.  On SIDs, TERPS is only guaranteeing terrain clearances (and therefore prescribes minimum climb gradients if it requires more than standard).

[Copper. 78]

hhahaha

 

interesting you mention that company

 

IRL with the B738 SOP is to arm LNAV VNAV at the gate before push back, which is a procedure I adopt in the sim and it works very well.

 

They don't arm VNAV on the ground, IRL.

 

Brian Nellis

[Porthos 9]

They don't arm VNAV on the ground, IRL.

 

Brian Nellis

Well Brian that must have changed in the last 3 years then. I stand corrected .

You don't need to be on a SID or Autopilot to make a turn, and it has nothing to do with TERPS requirements for which the aircraft is certified to be able to turn at a minimum altitude.  On SIDs, TERPS is only guaranteeing terrain clearances (and therefore prescribes minimum climb gradients if it requires more than standard).

 

Greg thats correct in some instances ..TERPS (though I am more familiar with ICAO PANSOPS) does provide terrain clearance. There are however minimum altitudes at which an aircraft must be before commencing a turn.

[E6BAV8R 88]

Greg thats correct in some instances ..TERPS (though I am more familiar with ICAO PANSOPS) does provide terrain clearance. There are however minimum altitudes at which an aircraft must be before commencing a turn.

 

Yes, there is.  However, it has to deal with aircraft certification and nothing to do with TERPS (assuming you aren't on a SID that requires a higher climb gradient).  Irrespective of minimum prescribed climb gradients via TERPS, minimum turn altitudes are a part of certification; just as minimum altitude for autopilot usage.

[Spin737 102]

Yes, there is.  However, it has to deal with aircraft certification and nothing to do with TERPS (assuming you aren't on a SID that requires a higher climb gradient).  Irrespective of minimum prescribed climb gradients via TERPS, minimum turn altitudes are a part of certification; just as minimum altitude for autopilot usage.

I've got the 400' minimum AEH (autopilot engagement height) in my Limitations. Can't find anything about turns in my AFM.

 

FAR 121.189 and AC120-91, JAR-OPS 1.495 and ICAO Annex 6 address the issue as an obstacle clearance issue based on climb performance dictated by the turning methods.

[E6BAV8R 88]

I've got the 400' minimum AEH (autopilot engagement height) in my Limitations. Can't find anything about turns in my AFM.

 

FAR 121.189 and AC120-91, JAR-OPS 1.495 and ICAO Annex 6 address the issue as an obstacle clearance issue based on climb performance dictated by the turning methods.

 

Which airplane?  I'd have to search around to find an AFM, but I believe the B-747 autopilot engagement is authorized at 250'.  The OEM will have a minimum authorized altitude certified by the FAA but individual operators can, of course, increase that.

[Spin737 102]

Which airplane?  I'd have to search around to find an AFM, but I believe the B-747 autopilot engagement is authorized at 250'.  The OEM will have a minimum authorized altitude certified by the FAA but individual operators can, of course, increase that.

737. I can't find anything that talks about certification issues for turns. The only references I can find are performance data, which comes from TERPS and PAN-OPS. I'm not sure how all that correlates, to be honest.

 

You're saying you think there are altitudes for turns that the 737 was certified with that has nothing to do with obstacle/climb performance?

[penfold 0]

Hi Ithink you've probably got the answer by now, but if not I don't arm the L/Vnav until above 450ft. you have to arm the autopilot first ,then L/Vnav.

 

                     Best of luck   pontious