ACA & DA/MDA
Thread Starter
Join Date: Mar 2013
Location: UK
Posts: 166
Likes: 0
Received 0 Likes
on
0 Posts
ACA & DA/MDA
I would like to canvass opinions on a debrief given to me following an (MEP/IR) LPC by an experienced FIE and IR examiner. I was fairly heavily criticised at the time but after research would question his logic. My licence was signed off though.
1. On an asymmetric approach, he said that as long as flaps were not in the landing configuration then a go around could be initiated below ACA. His example was if the DA was below ACA then a landing would not be possible if the cloud was below ACA. My interpretation of ACA was you were committed to land.
2. On an EFATO with autopilot engaged, I disconnected and flew manually. The point made to me was that the autopilot can reduce workload so use it.
Interested to hear thoughts on these points. I've been self analysing myself and trying to get to the bottom of this.
1. On an asymmetric approach, he said that as long as flaps were not in the landing configuration then a go around could be initiated below ACA. His example was if the DA was below ACA then a landing would not be possible if the cloud was below ACA. My interpretation of ACA was you were committed to land.
2. On an EFATO with autopilot engaged, I disconnected and flew manually. The point made to me was that the autopilot can reduce workload so use it.
Interested to hear thoughts on these points. I've been self analysing myself and trying to get to the bottom of this.
Join Date: Sep 1999
Location: uk
Posts: 4
Likes: 0
Received 0 Likes
on
0 Posts
Hi
My understanding and test experience is below ACA then you are landing and should not go around. DA should never be below ACA
EFATO I would as you did fly manually get aircraft trimmed then re engage AP
Just my personal thoughts
Rgds
My understanding and test experience is below ACA then you are landing and should not go around. DA should never be below ACA
EFATO I would as you did fly manually get aircraft trimmed then re engage AP
Just my personal thoughts
Rgds
Join Date: Nov 2016
Location: Cumbria
Posts: 228
Likes: 0
Received 0 Likes
on
0 Posts
Broadlands.........
You should google 'the children of magenta' on you tube.
I'm not sure what type you were flying (enlighten us), but I personally agree with the children of magenta, that in emergencies or traffic conflight you should particuarly at low level, switch off the automation and including autothrottles fly everything manually. FLY THE AIRCRAFT.
Look up AF 447 and the Tarom A310 crash at Bucharest.
You should google 'the children of magenta' on you tube.
I'm not sure what type you were flying (enlighten us), but I personally agree with the children of magenta, that in emergencies or traffic conflight you should particuarly at low level, switch off the automation and including autothrottles fly everything manually. FLY THE AIRCRAFT.
Look up AF 447 and the Tarom A310 crash at Bucharest.
Thread Starter
Join Date: Mar 2013
Location: UK
Posts: 166
Likes: 0
Received 0 Likes
on
0 Posts
Homsap
It was not anything complicated, just an annual reval in a hired DA42.
I've seen the YouTube clip before but watching again is a useful reminder.
Asking around it appears the examiner has picked others up for not using the ap when on single engine, even though the poh says it should not be used.
It was not anything complicated, just an annual reval in a hired DA42.
I've seen the YouTube clip before but watching again is a useful reminder.
Asking around it appears the examiner has picked others up for not using the ap when on single engine, even though the poh says it should not be used.
ACA = Asymmetric Committal Altitude, the minimum altitude from which an asymmetric approach may be abandoned.
Which part of 'Committal' doesn't the Examiner understand?
As for DA below your ACA, if that's the case then an engine out allowance must surely be added to the DA? On the ME aeroplane I used to fly, we used to add 250 ft to the normal Decision Height for the failure case (so typically 450 ft), with a Visual Committal Height of 350 ft. Once at VCH, you were committed to land and would extend the flaps to the landing configuration. Although that was in a 4-engined aeroplane with a double engine failure, the principles are the same for OEI in a twin.
If the POH states that the AP should not be used during an asymmetric go-around, that's the end of the argument and the Examiner was clearly wrong.
Thankfully I never had to fly a light twin in civilian life, but some of the tales I've heard about Examiners and their approach to asymmetric go-arounds have been...surprising. For example, one 'oral question' was "What would you do if you were below ACA and the runway was suddenly blocked?" To which I suggested the answer "Watch out for the ******g asteroid that's about to hit!". Another asked what you would do in a twin if you had an engine fire which hadn't gone out and you couldn't see the runway at DA....
Which part of 'Committal' doesn't the Examiner understand?
As for DA below your ACA, if that's the case then an engine out allowance must surely be added to the DA? On the ME aeroplane I used to fly, we used to add 250 ft to the normal Decision Height for the failure case (so typically 450 ft), with a Visual Committal Height of 350 ft. Once at VCH, you were committed to land and would extend the flaps to the landing configuration. Although that was in a 4-engined aeroplane with a double engine failure, the principles are the same for OEI in a twin.
If the POH states that the AP should not be used during an asymmetric go-around, that's the end of the argument and the Examiner was clearly wrong.
Thankfully I never had to fly a light twin in civilian life, but some of the tales I've heard about Examiners and their approach to asymmetric go-arounds have been...surprising. For example, one 'oral question' was "What would you do if you were below ACA and the runway was suddenly blocked?" To which I suggested the answer "Watch out for the ******g asteroid that's about to hit!". Another asked what you would do in a twin if you had an engine fire which hadn't gone out and you couldn't see the runway at DA....
Autopilot Limitations
Usable Speed Range 90 –> 180 KIAS Min Height (APP & DEP Phase) 200′ AGL Min Height (All Other Phases) 800′ AGL Min Height (Altitude Select Capture) 200′ AGL
The autopilot and yaw damper must be disconnected during takeoff, landing and OEI operations.
Usable Speed Range 90 –> 180 KIAS Min Height (APP & DEP Phase) 200′ AGL Min Height (All Other Phases) 800′ AGL Min Height (Altitude Select Capture) 200′ AGL
The autopilot and yaw damper must be disconnected during takeoff, landing and OEI operations.
Join Date: Nov 2016
Location: Cumbria
Posts: 228
Likes: 0
Received 0 Likes
on
0 Posts
Broadlands......
It does concern me in respect of the debrief, I am not familiar with the DA42, but I agree with 500 above, best to hand fly it. I have to say on my initial multi IR in a light twin, in the debrief the CAA staff examiner, questions my setting of altimeters. I was using number one for zone QNH/QFE/1013 and number two regional QNH, as in the abscence of RAD ALT, for terrain clearance, I will never under why the examiner had a issue setting regional QNH on number two.
It does concern me in respect of the debrief, I am not familiar with the DA42, but I agree with 500 above, best to hand fly it. I have to say on my initial multi IR in a light twin, in the debrief the CAA staff examiner, questions my setting of altimeters. I was using number one for zone QNH/QFE/1013 and number two regional QNH, as in the abscence of RAD ALT, for terrain clearance, I will never under why the examiner had a issue setting regional QNH on number two.
Join Date: Aug 2000
Location: Near Stuttgart, Germany
Posts: 1,095
Likes: 0
Received 1 Like
on
1 Post
Interesting thread... In almost 30 years of flying and instructing on piston twins I have not come across this "ACA" thing. Not in any aircraft manual nor in any of the training manuals of the schools I trained in and worked for. On the contrary, almost every light twin I have flown has a "ba(u)lked landing climb" table of graph in it's manual with figures for the single-engine go-around at very low level and they all start at 0ft, not some "ACA" value. Is that an UK thing or did I miss something important all those years?
And regarding the autopilot: Every AFM I know states "Autopilot: disengage" after an engine failure. Some allow the autopilot to be re-engaged after the aircraft has been configured and trimmed for single-engine flight, others don't. Although not being one of those magenta children I would agree with the examiner that an autopilot which is capable of and approved for single engine flight should be used as soon as practical to alleviate the workload.
And regarding the autopilot: Every AFM I know states "Autopilot: disengage" after an engine failure. Some allow the autopilot to be re-engaged after the aircraft has been configured and trimmed for single-engine flight, others don't. Although not being one of those magenta children I would agree with the examiner that an autopilot which is capable of and approved for single engine flight should be used as soon as practical to alleviate the workload.
Join Date: Aug 2009
Location: Copenhagen
Posts: 150
Likes: 0
Received 0 Likes
on
0 Posts
I feel kind of the same. In all my years flying and instructing on (light)twins both private and commercial I have never ever seen an "ACA" value in any POH or SOP. So maybe I also missed something important?
But with the lowest minima being CAT-I at 200 feet I don't really see the point. None of the twins I fly (Seneca / Aztec / Navajo) would have any problems doing a missed approach on one engine from 200 feet (or even from 100 feet). So maybe the DA is always higher than ACA in a light twin? But how would you get the ACA value for a Seneca or a Navajo for example ?
Just out of curiosity, What is the ACA value for a D42, and is that taken from the POH ??
But with the lowest minima being CAT-I at 200 feet I don't really see the point. None of the twins I fly (Seneca / Aztec / Navajo) would have any problems doing a missed approach on one engine from 200 feet (or even from 100 feet). So maybe the DA is always higher than ACA in a light twin? But how would you get the ACA value for a Seneca or a Navajo for example ?
Just out of curiosity, What is the ACA value for a D42, and is that taken from the POH ??
Join Date: May 2017
Location: UK
Posts: 76
Likes: 0
Received 0 Likes
on
0 Posts
1) If an ACA has been nominated, such that the pilot - for whatever reason - is unable to successfully go around below said ACA, then this should take into account the configuration at the time. Once below the nominated ACA then flap setting becomes less relevant, since the pilot has already decided that a go around is less likely to result in success. Many light twins will lose some height while transitioning from a stable approach to an asymmetric climb.
2) The autopilots fitted to all generations of DA42 (KAP140 or GFC700) are specifically prohibited from use in single engine scenarios in the POH.
Glad to hear your ratings were endorsed post-flight. Changing the result based on either of the debrief points mentioned would have been highly risky!
2) The autopilots fitted to all generations of DA42 (KAP140 or GFC700) are specifically prohibited from use in single engine scenarios in the POH.
Glad to hear your ratings were endorsed post-flight. Changing the result based on either of the debrief points mentioned would have been highly risky!
Guest
Posts: n/a
Just out of curiosity:
Whn reaching the ACA-does this not mean that from thisnaltitude on, the approach is no longer asymetrical?
Hence the DA can be below the ACA, as the asymetrical approach ends at the ACA, and continues as a normal approach down to the DA?
Whn reaching the ACA-does this not mean that from thisnaltitude on, the approach is no longer asymetrical?
Hence the DA can be below the ACA, as the asymetrical approach ends at the ACA, and continues as a normal approach down to the DA?
hueyracer wrote:
No - that would only be true if the approach was continued at idle power on the remaining engine. Which is highly unlikely.
DA simply cannot be below ACA. If the aircraft has a published ACA, then it must also have an EOA so that DA will always be above the ACA.
Whn reaching the ACA-does this not mean that from thisnaltitude on, the approach is no longer asymetrical?
DA simply cannot be below ACA. If the aircraft has a published ACA, then it must also have an EOA so that DA will always be above the ACA.
Join Date: Sep 1999
Location: uk
Posts: 4
Likes: 0
Received 0 Likes
on
0 Posts
HOMSAP
That is not quite the same scenario
With EFATO the problem is known, so sort out problem then when you are happy use AP to help you eg as you get approach set up or divert organised
That is not quite the same scenario
With EFATO the problem is known, so sort out problem then when you are happy use AP to help you eg as you get approach set up or divert organised
Last edited by vetflyer; 20th May 2017 at 09:40.
Join Date: Sep 1999
Location: uk
Posts: 4
Likes: 0
Received 0 Likes
on
0 Posts
Homsap
again I think that Kegworth is not the correct analogy It was not an EFATO and lots of factors involved not just inappropriate use of AP
All I can say that on my current a/c the ops manual say s you can engage AP after an EFATO but you need to manually trim a/c first. Gives time to run checklist to confirm the memory items
Rgds
again I think that Kegworth is not the correct analogy It was not an EFATO and lots of factors involved not just inappropriate use of AP
All I can say that on my current a/c the ops manual say s you can engage AP after an EFATO but you need to manually trim a/c first. Gives time to run checklist to confirm the memory items
Rgds
Join Date: May 2006
Location: UK
Posts: 53
Likes: 0
Received 0 Likes
on
0 Posts
The recommended ACA for light twins used to be 300' agl. The 300' used to be referred to as an 'engine out allowance'. The general idea was that if you commenced a single engine go-around in a light twin (any light twin) from 300' agl you'd be able to execute the manoeuvre without hitting the ground! So in principle it was good guidance, best practice if you will.
In reality most modern light twins don't need the full 300' and so the guidance (EOA)was gotten rid of. This then allowed CAA examiners to test down to lower limits hence the confusion surrounding ACA and where it came from.
In reality most modern light twins don't need the full 300' and so the guidance (EOA)was gotten rid of. This then allowed CAA examiners to test down to lower limits hence the confusion surrounding ACA and where it came from.
It is many years since I did my MEP but if I recall the logic was, in the event of a single engine go around, apply max allowable on the operating engine but if you pitched up with gear down and possibly flap approach, it would decelerate rapidly, so the idea of the ACA was it gave you sufficient height above the ground to keep descending whilst you clean up , remove the drag, then pitch up clean and endeavour to climb away at the 1-200 fpm or whatever the light twin would manage. Bearing in mind the initial MEP was a class rating conducted VFR so no DA involved.
Memory could be fuzzy due to the passing years.....
Memory could be fuzzy due to the passing years.....
Join Date: Nov 2016
Location: Cumbria
Posts: 228
Likes: 0
Received 0 Likes
on
0 Posts
Vetflyer.. you are in a sence correct as Kegworth didn't start at low level, so the under magenta children thesis, automaton can be apprpopriate, despite the fact in AF447 the automated systems probable compounded everything. Whatever happended to power, attitude, and configuration equals performance.
Join Date: Aug 2009
Location: Hogwarts
Posts: 35
Likes: 0
Received 0 Likes
on
0 Posts
From CAP 804:
(11)Asymmetric committal height:
(i) Asymmetric committal height is the minimum height needed to establish a positive climb whilst maintaining adequate speed for control and removal of drag during an approach to a landing.
Because of the significantly reduced performance of many CS-23 aeroplanes when operating on one engine, consideration is to be given to a minimum height from which it would be safely possible to attempt a go-around procedure, during an approach when the flight path will have to be changed from a descent to a climb with the aeroplane in a high drag con guration.
Due to the height loss which will occur during the time that the operating engine is brought up to full power, landing gear and ap retracted, and the aeroplane established in a climb at vyse a minimum height (often referred to as ‘asymmetric committal height’) is to be selected, below which the pilot should not attempt to take the aeroplane round again for another circuit. This height will be compatible with the aeroplane type, all up weight, altitude of the aerodrome being used, air temperature, wind, the height of obstructions along the climb out path, and pilot competence.
(11)Asymmetric committal height:
(i) Asymmetric committal height is the minimum height needed to establish a positive climb whilst maintaining adequate speed for control and removal of drag during an approach to a landing.
Because of the significantly reduced performance of many CS-23 aeroplanes when operating on one engine, consideration is to be given to a minimum height from which it would be safely possible to attempt a go-around procedure, during an approach when the flight path will have to be changed from a descent to a climb with the aeroplane in a high drag con guration.
Due to the height loss which will occur during the time that the operating engine is brought up to full power, landing gear and ap retracted, and the aeroplane established in a climb at vyse a minimum height (often referred to as ‘asymmetric committal height’) is to be selected, below which the pilot should not attempt to take the aeroplane round again for another circuit. This height will be compatible with the aeroplane type, all up weight, altitude of the aerodrome being used, air temperature, wind, the height of obstructions along the climb out path, and pilot competence.
Last edited by Albus_Dumbledore; 22nd May 2017 at 11:13. Reason: spelling
