CAT II app -737
Join Date: Dec 2003
Location: Dubai
Posts: 212
Likes: 0
Received 0 Likes
on
0 Posts
My previous post was not accurate since I was not able to check the B 737 NG AFM.
Basically the concept of CAT II and III has all to do with the definitions of “Fail Passive” and “Fail active” autopilot systems.
According to the B 737 NG AFM one needs both Autopilots to do a cat II and this implies that an automatic landing is the only option.
If a technical failure arises AFTER you have passed the approach ban then you have to abort the approach.
On the B 737 EFIS a cat II single channel was allowed and I do not see why it has changed on the B 737 NG.
Maybe the increased risk of tail strike has something to do with this ???
Anyone can shed some light on this ?
Basically the concept of CAT II and III has all to do with the definitions of “Fail Passive” and “Fail active” autopilot systems.
According to the B 737 NG AFM one needs both Autopilots to do a cat II and this implies that an automatic landing is the only option.
If a technical failure arises AFTER you have passed the approach ban then you have to abort the approach.
On the B 737 EFIS a cat II single channel was allowed and I do not see why it has changed on the B 737 NG.
Maybe the increased risk of tail strike has something to do with this ???
Anyone can shed some light on this ?
Thread Starter
Join Date: Aug 2001
Location: Europe-the sunshine side
Posts: 755
Likes: 0
Received 0 Likes
on
0 Posts
cap56 :that is why I've started the topic. On the 737 Clasic also,single chanel Cat 2 is not allowed.Only dual chanel with manual landing or autoland.
Cat 1 app is allowed with SCh,Dch or FD manual app.
I've found all this restrictions written in the AFM,so it is established by Boeing,not by the SOP.
Cat 1 app is allowed with SCh,Dch or FD manual app.
I've found all this restrictions written in the AFM,so it is established by Boeing,not by the SOP.
The essential elements required for an approach system are much more than the auto flight computer, sensors, etc. I recall that there are electrical distribution differences between 73 and NG aircraft. The changes were essential to get approval for a fail operational system.
Also beware the dual Rad Alt failure – revert to Cat 1. Some aircraft use Rad Alt to schedule gain changes in the FD as well as the autopilot, thus although the aircraft is Cat 1 capable the FD performance may not be very good.
Also beware the dual Rad Alt failure – revert to Cat 1. Some aircraft use Rad Alt to schedule gain changes in the FD as well as the autopilot, thus although the aircraft is Cat 1 capable the FD performance may not be very good.
Join Date: Dec 2003
Location: Dubai
Posts: 212
Likes: 0
Received 0 Likes
on
0 Posts
alexban
On the B 737 EFIS a cat I with manual landing was allowed if Autopilot was not disconnected before 80% of the DH.
Basically Boeing is not responsivble to set the limits. Boeing has to prove under what conditions the aircraft is fail passive or fail operational.
The certifing authority then approves the capability.
On the B 737 EFIS a cat I with manual landing was allowed if Autopilot was not disconnected before 80% of the DH.
Basically Boeing is not responsivble to set the limits. Boeing has to prove under what conditions the aircraft is fail passive or fail operational.
The certifing authority then approves the capability.
Cat IIIb in a 737
Just to answer a previous query raised about Cat IIIb on the 737, it has been available for about a year.
To be honest I don’t know what the physical differences to the aircraft are but on the flightdeck you will see an extra MFD button labelled “C/R” (Clear / Recall), this must be pressed before every Cat IIIb approach to check the systems. The result will be a message on the upper DU which will either say “RECALL” which is OK or "NO LAND 3" or "NO AUTOLAND". Note Cat IIIa is still possible with a NO LAND 3 advisory. In this case green "LAND 2" annunciations will appear on both outboard display units. When established on the Cat IIIb approach you will get a ROLLOUT armed annunciation underneath VOR/LOC in the same way that you get FLARE armed under G/S for a Cat IIIa. More details at
www.b737.org.uk/flightinsts.htm
Note, aircraft with this mod are able to autoland with one engine out – v. impressive!
Cat II in a 737
To answer the question of the thread; all 737’s are certified for Cat II manual landings but it is up to the individual operator to approve and train their crews to do this. None of the 737 operators I have flown with have chosen to do this and to be honest I am grateful.
S & L
To be honest I don’t know what the physical differences to the aircraft are but on the flightdeck you will see an extra MFD button labelled “C/R” (Clear / Recall), this must be pressed before every Cat IIIb approach to check the systems. The result will be a message on the upper DU which will either say “RECALL” which is OK or "NO LAND 3" or "NO AUTOLAND". Note Cat IIIa is still possible with a NO LAND 3 advisory. In this case green "LAND 2" annunciations will appear on both outboard display units. When established on the Cat IIIb approach you will get a ROLLOUT armed annunciation underneath VOR/LOC in the same way that you get FLARE armed under G/S for a Cat IIIa. More details at
www.b737.org.uk/flightinsts.htm
Note, aircraft with this mod are able to autoland with one engine out – v. impressive!
Cat II in a 737
To answer the question of the thread; all 737’s are certified for Cat II manual landings but it is up to the individual operator to approve and train their crews to do this. None of the 737 operators I have flown with have chosen to do this and to be honest I am grateful.
S & L
Join Date: May 2004
Location: UK
Posts: 54
Likes: 0
Received 0 Likes
on
0 Posts
Fail operational = the initial condition of a 3 autopilot system, a failure would mean the autoland is still OPERATIONAL. LAND 2
Fail Passive = A second failure of a 3 a/p system would leave only one A/P resulting in a fail passive meaning a subsequent fail would leave the aircarft in a passive condition.
my expirience is of only 3 chanel systems, i do belive however that the 737 is capable of fail operational with some magic it does!
Fail Passive = A second failure of a 3 a/p system would leave only one A/P resulting in a fail passive meaning a subsequent fail would leave the aircarft in a passive condition.
my expirience is of only 3 chanel systems, i do belive however that the 737 is capable of fail operational with some magic it does!
Join Date: May 2004
Location: UK
Posts: 54
Likes: 0
Received 0 Likes
on
0 Posts
CAP 56
CAT 3 is separated,
CAT 3a requires fail passive or fail operational autopilot.
CAT 3b Requires fail operational autopilot.
I am aware that the 737 can carry out CAT 3a, allthought with what ive learned, it is fail operational so it could do 3b. Im not sure how but im trying to find out at work how a 2 autopilot system can be fail operational.
safteypee i think got it when he mentioned the bus isolation on the 737. The 747 and 777 does this too. splits the buss supply to the AFDS into independant supplys, the 737 does this too and thats partly how it can achive fail operational 3b.
This is an intresting thread where im learning too, more on the operational side of autoland. im a licenced avionic eng and i like to know how the ops side of things are as well as the tech.
i hate the way ppl get so aggressive in forums you said to me "Your wrong", a very strong statment. pls read your post again. please be a bit more courteous no one knows it all. Any who claim too are fools and id be scared if they were pilot or engineer!
Rgds
Stuart
CAT 3 is separated,
CAT 3a requires fail passive or fail operational autopilot.
CAT 3b Requires fail operational autopilot.
I am aware that the 737 can carry out CAT 3a, allthought with what ive learned, it is fail operational so it could do 3b. Im not sure how but im trying to find out at work how a 2 autopilot system can be fail operational.
safteypee i think got it when he mentioned the bus isolation on the 737. The 747 and 777 does this too. splits the buss supply to the AFDS into independant supplys, the 737 does this too and thats partly how it can achive fail operational 3b.
This is an intresting thread where im learning too, more on the operational side of autoland. im a licenced avionic eng and i like to know how the ops side of things are as well as the tech.
i hate the way ppl get so aggressive in forums you said to me "Your wrong", a very strong statment. pls read your post again. please be a bit more courteous no one knows it all. Any who claim too are fools and id be scared if they were pilot or engineer!
Rgds
Stuart
Cap 56 life is not that easy; “Basically Boeing is not responsible to set the limits. Boeing has to prove under what conditions the aircraft is fail passive or fail operational. The certifying authority then approves the capability.”
The manufacturer has to determine the accuracy and reliability of the auto flight system to enable low vis operations. In addition the autopilot minimum use height has to be assessed (often a function of nose down failures, hence one use of trim up); in some aircraft the min use ht does not enable the lowest DH if the 80% rule is used, which for JAA operators only applies to Cat 2 and not Cat 1. (Appendix 1 to JAR-OPS 1.430). The autopilot min use ht should be published in the AFM and for FAA based AFMs there is usually a diagram showing the failure case recovery trajectory – check the assumptions made about this for your aircraft and for the recovery maneuver (1.3 g pull up?). Thus the Manufacturers limit may supercede the regulatory limit, and with a higher DH the RVR minima are also higher.
FunctionedSatis there is enormous scope for confusion between certification requirements and operating requirements; the generally accepted ICAO definitions were replaced some time ago by muddled thinking, mainly by the operational regulators (JAR-OPS).
JAR-AWO (equipment certification) is one of the better regulatory documents, it divides the categories by DH (100 / 50 / <50 ft), or no DH, and any rollout guidance requirements.
The RVR minima (visual cues) are operational limits; these are in a messy section (E) of JAR-OPS. However, with improving technology the boundaries of the minima are being eroded. i.e A ‘Super Fail Passive’ Cat 3 autopilot (still a fail passive system) may operate in 150 m RVR, which is considered Cat 3b visibility territory (Avro RJ), but the DH remains at 50 ft. Whereas Cat 3a 50 ft / 200-300 RVR allows a manual landing following failure, operations in 150 RVR mandate a GA after the failure.
The best advice is to read the manual, check the MMEL, and don’t assume anything.
The manufacturer has to determine the accuracy and reliability of the auto flight system to enable low vis operations. In addition the autopilot minimum use height has to be assessed (often a function of nose down failures, hence one use of trim up); in some aircraft the min use ht does not enable the lowest DH if the 80% rule is used, which for JAA operators only applies to Cat 2 and not Cat 1. (Appendix 1 to JAR-OPS 1.430). The autopilot min use ht should be published in the AFM and for FAA based AFMs there is usually a diagram showing the failure case recovery trajectory – check the assumptions made about this for your aircraft and for the recovery maneuver (1.3 g pull up?). Thus the Manufacturers limit may supercede the regulatory limit, and with a higher DH the RVR minima are also higher.
FunctionedSatis there is enormous scope for confusion between certification requirements and operating requirements; the generally accepted ICAO definitions were replaced some time ago by muddled thinking, mainly by the operational regulators (JAR-OPS).
JAR-AWO (equipment certification) is one of the better regulatory documents, it divides the categories by DH (100 / 50 / <50 ft), or no DH, and any rollout guidance requirements.
The RVR minima (visual cues) are operational limits; these are in a messy section (E) of JAR-OPS. However, with improving technology the boundaries of the minima are being eroded. i.e A ‘Super Fail Passive’ Cat 3 autopilot (still a fail passive system) may operate in 150 m RVR, which is considered Cat 3b visibility territory (Avro RJ), but the DH remains at 50 ft. Whereas Cat 3a 50 ft / 200-300 RVR allows a manual landing following failure, operations in 150 RVR mandate a GA after the failure.
The best advice is to read the manual, check the MMEL, and don’t assume anything.
Join Date: May 2002
Location: Who can say?
Posts: 1,700
Likes: 0
Received 0 Likes
on
0 Posts
FunctionedSatis - I note your comments about Cap56's comments and, like you, I found them on first reading aggressive and rude.
I am minded to issue a warning to posters yet again about the tenor of comments, questions and answers posted here. If you can't keep it polite and professional, then please don't bother to post. Go somewhere that adolescent behaviour is appreciated.
Cap56, I will leave off a personal warning to you as I am not aware of previous history on your part, and I realise that English may not be your first language.
{edit} On second thoughts, after seeing his contribution to the Balanced Field thread, Cap56 is banned from this forum.
I am minded to issue a warning to posters yet again about the tenor of comments, questions and answers posted here. If you can't keep it polite and professional, then please don't bother to post. Go somewhere that adolescent behaviour is appreciated.
Cap56, I will leave off a personal warning to you as I am not aware of previous history on your part, and I realise that English may not be your first language.
{edit} On second thoughts, after seeing his contribution to the Balanced Field thread, Cap56 is banned from this forum.
Last edited by Captain Stable; 2nd Sep 2004 at 20:26.
Join Date: May 2004
Location: UK
Posts: 54
Likes: 0
Received 0 Likes
on
0 Posts
I have some information.
From the Boeing 737-300/400/500 Maintenance manual chapter 22 Autoflight.
(Operator BA)
Quote
" The Autoland system installed on BAB 737 is cleared for CAT 3A operation with the folowing limits:- DH=50ft RVR=200meters."
This would indicate to me that the 737 is a fail passive system.
As for the next generation types i have no idea an no access to any information.
Safteypee, thanks for that, very intresting i might try to get a read at JAR OPS JAR AWO.
Rgds
Stu.
From the Boeing 737-300/400/500 Maintenance manual chapter 22 Autoflight.
(Operator BA)
Quote
" The Autoland system installed on BAB 737 is cleared for CAT 3A operation with the folowing limits:- DH=50ft RVR=200meters."
This would indicate to me that the 737 is a fail passive system.
As for the next generation types i have no idea an no access to any information.
Safteypee, thanks for that, very intresting i might try to get a read at JAR OPS JAR AWO.
Rgds
Stu.
Last edited by FunctionedSatis; 2nd Sep 2004 at 23:59.
