B737 autopilot
Joined: Mar 2001
Posts: 4,563
Likes: 35
From: I wouldn't know.
My FCOM states:
[737-300/400/500]
Do not engage the autopilot for takeoff below 1000ft AGL
[737-700/800]
Do not engage the autopilot for takeoff below 400 ft AGL.
Since we do mainly fly the classics (first NG arrives in around 10 days) our SOPs still require to handfly on a normal take off or single engine take off until we have cleaned up the aircraft.
Since all ILS approaches are flown with dual autopilots a normal go-around before we switch to manual flight will be fully automatical which reduces the workload considerably. However switching to manual flight is encouraged before 400ft so we do not have to fight the trimming forces. Personally i switch to manual flight way before that (either raw data from the beginning or manual after GS intercept), except if visibility is marginal and a go-around is likely.
[737-300/400/500]
Do not engage the autopilot for takeoff below 1000ft AGL
[737-700/800]
Do not engage the autopilot for takeoff below 400 ft AGL.
Since we do mainly fly the classics (first NG arrives in around 10 days) our SOPs still require to handfly on a normal take off or single engine take off until we have cleaned up the aircraft.
Since all ILS approaches are flown with dual autopilots a normal go-around before we switch to manual flight will be fully automatical which reduces the workload considerably. However switching to manual flight is encouraged before 400ft so we do not have to fight the trimming forces. Personally i switch to manual flight way before that (either raw data from the beginning or manual after GS intercept), except if visibility is marginal and a go-around is likely.
Joined: Apr 2005
Posts: 1,415
Likes: 9
From: Australia
Since all ILS approaches are flown with dual autopilots
On the other hand a single autopilot ILS can be flown within the same flight path accuracy as a dual autopilot ILS to the minimum disconnect height of 50 ft and if not visual the autopilot is disconnected and a manual GA conducted. There is simply no point to making a dual autopilot approach just because a GA may be needed. So what? A competent pilot should have already been certified to conduct manually flown go-arounds both all engines and one engine inoperative. The danger is disconnecting the dual autopilots below 400 ft when landing is assured and then being caught by the significant mis-trim which was automatically applied on dual autopilot at 400 ft.
Thread Starter
Joined: Jun 2000
Posts: 4,507
Likes: 4
From: last time I looked I was still here.
A37575:
To answer you first. I had heard some some curious 'go their own way' pilots who did this as a matter of course. Very non-standard. They considered that in the event of a G/A they would have the luxury of an A/P G/A. They did this even in VMC conditions on the assumption that they would disconnect before the nose-up trim was introduced. I agree with your sentiments about flying abilities.
Denti:
Your C.P seems to be misguided in many matters. A dual A/P approach with a requirement to disconnect before 400'agl. Hm? Curious. What consideration is given to Wx & minima? Close to Cat 1 on a Cat 1 installation? But then a man land? What do you do for a NPA? What do you do for a visual approach? Either you can fly a manual G/A or you can't!
Secondly; and back to my original question, and your company seems a classic example of misusing the NG a/c. You are flying a dual A/P approach expecting a manual landing. Requirement to disconnect before 400' agl. You also fly an NG a/c certified to engage the A/P at 400' agl on departure but you do not do so until flaps up. Why?
Somewhere I am missing something because this seems a crass condradiction of not using the a/c the way it was designed.
People: Why do we wait until Flaps up before engaging the A/P?
And once again: If the A/P will descend the a/c before ALT HLD so will the F.D. but it wont. It will accelerate in level flight V/S = zero to regain speed if below V2. It will desend if you do not fly the FD accurately.
And to answer A37575's earlier post about hand flying on departure. And Oh dear Mad Macho MIke has been Munching on the Crunchy bars and Cracking coconuts between his biceps again. The old argument of Right stuff versus common sense. I can, if I want to, fly the Red Bull air race course inverted with one eye closed. No bother. I might kill myself, and hopefully only myself.
On a dark !!!!ty night with a major failure, siiting at the sharp end of an aluminium tube full of pax + me, is not the time to show a 500 hr sprog what a Top Gun star I am. It is the time to use whatever resources are at hand to deliver all said & sundry to terra firma in one piece with no more broken than the original failure. That is what medals are won for. Scaring !!!! out of myself is left for days off in the right type of a/c on my own. If the A/P is broke I can handle it, but if it ain't broke then I am expected to use it. The F.D. is certified down below CAT 1 minima. Will anyone stand up and advocate flying LVO manually? Nuff said.
A skillful pilot is one who uses his skill to aviod situations where his skilled is needed to extricate himself.
Can anyone answer the original question from a technical reason?
To answer you first. I had heard some some curious 'go their own way' pilots who did this as a matter of course. Very non-standard. They considered that in the event of a G/A they would have the luxury of an A/P G/A. They did this even in VMC conditions on the assumption that they would disconnect before the nose-up trim was introduced. I agree with your sentiments about flying abilities.
Denti:
Your C.P seems to be misguided in many matters. A dual A/P approach with a requirement to disconnect before 400'agl. Hm? Curious. What consideration is given to Wx & minima? Close to Cat 1 on a Cat 1 installation? But then a man land? What do you do for a NPA? What do you do for a visual approach? Either you can fly a manual G/A or you can't!
Secondly; and back to my original question, and your company seems a classic example of misusing the NG a/c. You are flying a dual A/P approach expecting a manual landing. Requirement to disconnect before 400' agl. You also fly an NG a/c certified to engage the A/P at 400' agl on departure but you do not do so until flaps up. Why?
Somewhere I am missing something because this seems a crass condradiction of not using the a/c the way it was designed.
People: Why do we wait until Flaps up before engaging the A/P?
And once again: If the A/P will descend the a/c before ALT HLD so will the F.D. but it wont. It will accelerate in level flight V/S = zero to regain speed if below V2. It will desend if you do not fly the FD accurately.
And to answer A37575's earlier post about hand flying on departure. And Oh dear Mad Macho MIke has been Munching on the Crunchy bars and Cracking coconuts between his biceps again. The old argument of Right stuff versus common sense. I can, if I want to, fly the Red Bull air race course inverted with one eye closed. No bother. I might kill myself, and hopefully only myself.
On a dark !!!!ty night with a major failure, siiting at the sharp end of an aluminium tube full of pax + me, is not the time to show a 500 hr sprog what a Top Gun star I am. It is the time to use whatever resources are at hand to deliver all said & sundry to terra firma in one piece with no more broken than the original failure. That is what medals are won for. Scaring !!!! out of myself is left for days off in the right type of a/c on my own. If the A/P is broke I can handle it, but if it ain't broke then I am expected to use it. The F.D. is certified down below CAT 1 minima. Will anyone stand up and advocate flying LVO manually? Nuff said.
A skillful pilot is one who uses his skill to aviod situations where his skilled is needed to extricate himself.
Can anyone answer the original question from a technical reason?
Joined: Jan 2005
Posts: 303
Likes: 56
From: Europe
Our company operates both classics and NGs. Our SOPs prescribe a minimum AP engagement altitude of 1000 feet for both types, just to standardise on the lowest common denominator (being the classics). I think differentiating between the classics (certified above 1000 feet) and NGs (certified above 400 feet) would just increase the chances of inadvertent mistakes without offering any significant operational or safety benefits. We also use 1000 feet as the minimum AP engagement altitude in case of an engine failure during takeoff.
In the simulator the autopilot may slowly descend during one-engine acceleration. It shouldn't, but it does, sometimes. Especially if the engine failure occurs during a reduced thrust takeoff and the crew does not set maximum takeoff thrust on the operating engine. This might be more of a problem for the classics than the NGs, but still. However, I don't know if this simulator behaviour is realistic - never had an engine failure in real life.
In the simulator the autopilot may slowly descend during one-engine acceleration. It shouldn't, but it does, sometimes. Especially if the engine failure occurs during a reduced thrust takeoff and the crew does not set maximum takeoff thrust on the operating engine. This might be more of a problem for the classics than the NGs, but still. However, I don't know if this simulator behaviour is realistic - never had an engine failure in real life.
Joined: Mar 2001
Posts: 4,563
Likes: 35
From: I wouldn't know.
RAT 5 you have to read a tad more carefully 
As i said at the moment we operate purely Classics with the first NG arriving in around 10 days.
As i said above, it is recommendet to switch to manual flight before 400 ft AGL if you intend to do a manual landing, however you can happily let it fly down to 50ft and then disconnect for that, in fact that is actually trained to show us the effect of the trim up which is not at all hard to overcome if you are prepared. Of course that only applies to ILS, NPAs and visuals are flown with single autopilot or raw data. Raw data flying is heavily encouraged and i fly quite often into the london tma from cruising altitude manually and flight director off until touchdown.
Dual channel approach is recommendet because there is a possibility of a single channel autopilot hardover which actually happened in my company, if you use dual channel autopilot you wont get that but instead just a disconnect of both autopilots (every CAT D simulator can simulate that, just try it). As a plus you allways have automatic go-around capability and can allways switch to CAT II or III whenever you need to.
I have just rechecked and the autopilot actually may be used above minimum autopilot engagement altitude during take off, so 400ft in the NG is perfectly fine. That just recently changed in the ongoing standardization over the whole boeing fleet in our airline group and as i'm not officially trained on the NG yet (have to do a difference training consisting of CBT, selfstudy with a differences manual, written test, a simulator session and 5 days of supervision on the line) i wasn't really aware that with the NG our company now allows engagement at 400ft AGL.
As i said at the moment we operate purely Classics with the first NG arriving in around 10 days.
As i said above, it is recommendet to switch to manual flight before 400 ft AGL if you intend to do a manual landing, however you can happily let it fly down to 50ft and then disconnect for that, in fact that is actually trained to show us the effect of the trim up which is not at all hard to overcome if you are prepared. Of course that only applies to ILS, NPAs and visuals are flown with single autopilot or raw data. Raw data flying is heavily encouraged and i fly quite often into the london tma from cruising altitude manually and flight director off until touchdown.
Dual channel approach is recommendet because there is a possibility of a single channel autopilot hardover which actually happened in my company, if you use dual channel autopilot you wont get that but instead just a disconnect of both autopilots (every CAT D simulator can simulate that, just try it). As a plus you allways have automatic go-around capability and can allways switch to CAT II or III whenever you need to.
I have just rechecked and the autopilot actually may be used above minimum autopilot engagement altitude during take off, so 400ft in the NG is perfectly fine. That just recently changed in the ongoing standardization over the whole boeing fleet in our airline group and as i'm not officially trained on the NG yet (have to do a difference training consisting of CBT, selfstudy with a differences manual, written test, a simulator session and 5 days of supervision on the line) i wasn't really aware that with the NG our company now allows engagement at 400ft AGL.
Thread Starter
Joined: Jun 2000
Posts: 4,507
Likes: 4
From: last time I looked I was still here.
Denti: Thank you for your input and I apologise for any short-sightedness.
To others, many thanks for your contributions. I see there are those who engage A/P at 1000' agl and those who wait until Flaps Up. It seems that the difference is the whim of the Chief Pilot and company SOP's. OK; so we have a difference and neither is the Boeing design criteria.
My question still stands. Can anyone provide a technical reason why the Boeing design standard is not applied? I understand that those who operate a mix fleet of classics & NG's chose the lowest common denominator of
1000'. Fine. Why is the UKCAA cerification 1000' and the FAA 400'? Why, if the NG is 400' do those operators choose Flaps up? What is the technical reason?
I once flew for an operator who cleaned up at 1000' on a V1 cut, SE G/A & 2 engine G/A. Keep it simple and all the same. Seemed like a good idea. It is above Boeing minima. Then I flew for an operator who cleaned up at 1000' on a V1 cut & SE G/A but 400' on a 2 engine G/A because it was standard Boeing, but still waited until Flaps Up to engage A/P. You understand my wondering at people's thinking? They use some of standard Boeing Ops but not others in the same manoeuvre.
Why do we operate the a/c down to Boeing minima on landing close to the ground ( the rock hard place) but some choose to make their own minima when climbing away from the rock hard place? It beats me! How many people get an instruction manual for a micro-wave and then choose to do it differently?
To others, many thanks for your contributions. I see there are those who engage A/P at 1000' agl and those who wait until Flaps Up. It seems that the difference is the whim of the Chief Pilot and company SOP's. OK; so we have a difference and neither is the Boeing design criteria.
My question still stands. Can anyone provide a technical reason why the Boeing design standard is not applied? I understand that those who operate a mix fleet of classics & NG's chose the lowest common denominator of
1000'. Fine. Why is the UKCAA cerification 1000' and the FAA 400'? Why, if the NG is 400' do those operators choose Flaps up? What is the technical reason?
I once flew for an operator who cleaned up at 1000' on a V1 cut, SE G/A & 2 engine G/A. Keep it simple and all the same. Seemed like a good idea. It is above Boeing minima. Then I flew for an operator who cleaned up at 1000' on a V1 cut & SE G/A but 400' on a 2 engine G/A because it was standard Boeing, but still waited until Flaps Up to engage A/P. You understand my wondering at people's thinking? They use some of standard Boeing Ops but not others in the same manoeuvre.
Why do we operate the a/c down to Boeing minima on landing close to the ground ( the rock hard place) but some choose to make their own minima when climbing away from the rock hard place? It beats me! How many people get an instruction manual for a micro-wave and then choose to do it differently?
Last edited by RAT 5; 7th December 2007 at 22:59.
