B737 - Great Idea of using A/T in ARM mode for approach/landing.
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B737 - Great Idea of using A/T in ARM mode for approach/landing.
In our company I believe we're thinking of bringing in an option that you can keep the autothrottle engaged right down to after landing on a Cat I approach.
What you do, is disconnect the autopilot as usual, but keep the A/T engaged. You then press SPEED on the MCP. This disengages speed mode and puts it into ARM mode. This is the same mode that it goes to on a LVL CHG descent after RETARD. The A/T is passive - eg it does nothing and the thrust levers are yours. It is a manual thrust landing (the thrust levers can be manually positioned with no inteference from the A/T), and you can not tell that the A/T is engaged.
HOWEVER, it is there in the event of a GA, so you can press TOGA and the thrust levers will advance to the GA setting.
It sounds a VERY good idea, and I can not see any disadvantages. What I'm unclear about is whether you still get Windshear and low speed reversion protection. this would be an added benefit, but the tech. manual doesn't go deep enough to cover this.
What you do, is disconnect the autopilot as usual, but keep the A/T engaged. You then press SPEED on the MCP. This disengages speed mode and puts it into ARM mode. This is the same mode that it goes to on a LVL CHG descent after RETARD. The A/T is passive - eg it does nothing and the thrust levers are yours. It is a manual thrust landing (the thrust levers can be manually positioned with no inteference from the A/T), and you can not tell that the A/T is engaged.
HOWEVER, it is there in the event of a GA, so you can press TOGA and the thrust levers will advance to the GA setting.
It sounds a VERY good idea, and I can not see any disadvantages. What I'm unclear about is whether you still get Windshear and low speed reversion protection. this would be an added benefit, but the tech. manual doesn't go deep enough to cover this.
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What you suggest was SOP in Ansett when I last jumpseated with them and, I gather, also in many other 737 operators. The advantages are as you state, with min speed protection etc. It was suggested to your airline about five years ago but of course nothing happened. "We never did it on 707s/Viscounts/Argonauts/etc, so why should we do it now" is the usual response to anything innovative.
[This message has been edited by Hew Jampton (edited 06 May 2001).]
[This message has been edited by Hew Jampton (edited 06 May 2001).]
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MaxPete - The automatics must be disengaged at 140 feet when coupled to an ILS, 300 feet for a NPA. It is not SOPs to use A/T without the A/P, its all or nothing - you would not remember to disengage the A/T at 140' if hand flying.
The 737 is not as advanced as the fokker and when you press TOGA with the A/T disengaged you do not get A/T, only pitch commands from the F/D - you have to manually advance the thrust levers. It's difficult to find the right thrust setting initially in a high workload situation, and I suspect many put on more than the A/T 1st press of TOGA, just to be sure, so making things happen faster.
I like to be hand flying by 1500' if possible, to get a feel for it, and it would enable people to hand fly earlier, knowing you haven't lost anything for the G/A.
The 737 is not as advanced as the fokker and when you press TOGA with the A/T disengaged you do not get A/T, only pitch commands from the F/D - you have to manually advance the thrust levers. It's difficult to find the right thrust setting initially in a high workload situation, and I suspect many put on more than the A/T 1st press of TOGA, just to be sure, so making things happen faster.
I like to be hand flying by 1500' if possible, to get a feel for it, and it would enable people to hand fly earlier, knowing you haven't lost anything for the G/A.
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We use this mode (ie A/T in ARM) all the time.
If the A/T is engaged (ie switch is up) and speed is "deselected" you will have "ARM" showing in the top left of your EADI.
This means that you have low speed alpha protection (ie it will drop into "MCP Speed" mode if it deems the speed falls too low for the given weight). This can cause occasional problems as it errs of the VERY cautious side and so will kick in and advance the power when you least expect/want it.
It also given you high speed protection (ie will reduce power if you reach Vmo/Mmo). This mode should however never be seen in normal operations.
During the approach with the A/T in ARM if you press the TOGA button, TOGA will annunciate on the EADI and the thrust leavers will advance to the GA power setting.
All in all, it benefits leaving it in the Speed deselected mode (A/T armed for the appoach) in all but gusty conditions when it may have trouble coping, and keeping out of your way!
Hope this helps!
If the A/T is engaged (ie switch is up) and speed is "deselected" you will have "ARM" showing in the top left of your EADI.
This means that you have low speed alpha protection (ie it will drop into "MCP Speed" mode if it deems the speed falls too low for the given weight). This can cause occasional problems as it errs of the VERY cautious side and so will kick in and advance the power when you least expect/want it.
It also given you high speed protection (ie will reduce power if you reach Vmo/Mmo). This mode should however never be seen in normal operations.
During the approach with the A/T in ARM if you press the TOGA button, TOGA will annunciate on the EADI and the thrust leavers will advance to the GA power setting.
All in all, it benefits leaving it in the Speed deselected mode (A/T armed for the appoach) in all but gusty conditions when it may have trouble coping, and keeping out of your way!
Hope this helps!
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BmPilot,
We have been using this technique in our SOP since we started the B737 Classics almost 12 years ago and we have not had any problems with it.
The Handling Pilot usually calls for the Montioring Pilot to 'Deselect Speed' by pushing the SPEED button on the MCP when the A/P is disconnected.
The system descriptions and functions are exactly as mention by Sink Rate.
HS
We have been using this technique in our SOP since we started the B737 Classics almost 12 years ago and we have not had any problems with it.
The Handling Pilot usually calls for the Montioring Pilot to 'Deselect Speed' by pushing the SPEED button on the MCP when the A/P is disconnected.
The system descriptions and functions are exactly as mention by Sink Rate.
HS
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A word of caution. It has been known for the system to sense the trigger for power during the landing flare as the speed reduces, if this takes place before the (27' I think?) 'Retard' point. Can be a bit disconcerting. I have watched it happen to the other pilot and it doesn't half mess up the landing!
I think it works on 1.3xVstall, as sensed by the alpha vane. There are points in the approach profile (737) where (if ACCURATE +5kt speeds are flown - what!?) the trigger point is actually ABOVE Vref+5. This occurs at a few flap 30 weights and more flap 40s. Use with caution.
I think it works on 1.3xVstall, as sensed by the alpha vane. There are points in the approach profile (737) where (if ACCURATE +5kt speeds are flown - what!?) the trigger point is actually ABOVE Vref+5. This occurs at a few flap 30 weights and more flap 40s. Use with caution.
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Like practicaly every other 737 driver I deselect SPEED mode at some stage during the approach in good wx or light rain and leave the AT on (or off completley if maintaining raw data skills). But I do leave SPEED in all the way down to the deck in very heavy rain especialy during approaches at night onto short strips. It actualy does help back up your flare judgement when Natures throwing thick buckets of water and lightning in your face.
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In our company we also go that way. "Speed deselected - manual fight". 
But there two things to remember. First, if you decide to fly manual before glideslope capture, the speed mode comes active on capture and the present speed is displayed on MCp panel. You must deselect again and call for proper speed on MCP. So I use to take over manual after glideslope capture and the problem is solved.
The second point is the question of what speed is to be set on MCP when in landing configuration. The A/T-systems has a build in gust compensation so Vref+5 must be set on MCP. But in normal operation everybody does set the speed including correction for wind when in manual flight with speed deselected. For automatic approaches with autoland we set vref+5 on MCP. What is the right way?
But there two things to remember. First, if you decide to fly manual before glideslope capture, the speed mode comes active on capture and the present speed is displayed on MCp panel. You must deselect again and call for proper speed on MCP. So I use to take over manual after glideslope capture and the problem is solved.
The second point is the question of what speed is to be set on MCP when in landing configuration. The A/T-systems has a build in gust compensation so Vref+5 must be set on MCP. But in normal operation everybody does set the speed including correction for wind when in manual flight with speed deselected. For automatic approaches with autoland we set vref+5 on MCP. What is the right way?
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Gomind your dead right. But every experienced 737 pilot knows the AT is pretty hopeless at holding Vref+5 in crappy gusty wx. Its too damn wimpy when aggressive power corrections need to be made.
The Boeing line that the AT can hold speed and doesnt need wind correction factors is fine on a nice sunny Sunday morning with the birds chirping, but it isnt that fine when doing a VOR through the muck with 30kt+ winds varying all over the place.
The Boeing line that the AT can hold speed and doesnt need wind correction factors is fine on a nice sunny Sunday morning with the birds chirping, but it isnt that fine when doing a VOR through the muck with 30kt+ winds varying all over the place.
