TAM A320 crash at Congonhas, Brazil
Why is there no technology available that can provide the pilots with accurate and simple information on the deceleration rate of the aircraft on touch down?
Autobrake medium aims to provide 3 m/s/s deceleration. When it achieves at least 80% of this a little green "Decel" light comes on.
On landing, the PNF calls "Decel" when it comes on, or "No decel" if it doesn't.
The response would vary on the situation, but normally (assuming you really need to slow down) max reverse and apply footbrakes.
I'm not going to speculate, but I can tell you of something I saw once.
A pilot had just done an Airbus conversion, involving a lot of time in the sim doing single engined work. He was then online, with a single inop reverser. Just before landing, his colleague reminded him of the single inop reverser. As a result of concentrating hard, his addled brain made a sort of wrong connection and just retarded the single thrust lever (just like in the sim with all those single engined landings).
That pilot quickly realised something was wrong and then closed the other lever. No harm done. But it was on a very long, very wide and very dry runway.
And I thought I'd never tell anyone I'd done that..
Edit: this post was in response to a question "what would the pilots do next" which seems to have been deleted.
I'm not going to speculate, but I can tell you of something I saw once.
A pilot had just done an Airbus conversion, involving a lot of time in the sim doing single engined work. He was then online, with a single inop reverser. Just before landing, his colleague reminded him of the single inop reverser. As a result of concentrating hard, his addled brain made a sort of wrong connection and just retarded the single thrust lever (just like in the sim with all those single engined landings).
That pilot quickly realised something was wrong and then closed the other lever. No harm done. But it was on a very long, very wide and very dry runway.
And I thought I'd never tell anyone I'd done that..
Edit: this post was in response to a question "what would the pilots do next" which seems to have been deleted.
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early on in this thread, MAX braking was not a reccomended setting.
Is it the setting that would not reduce deceleration due to reverse?
and if so, I would think it was the one to use.
Is it the setting that would not reduce deceleration due to reverse?
and if so, I would think it was the one to use.
Why is there no technology available that can provide the pilots with accurate and simple information on the deceleration rate of the aircraft on touch down?
During critical phases of flight such as takeoff, initial climb, approach and landing the speed trend arrow is a very helpful indication of the changing longitudinal energy state of the aircraft.
On takeoff the trend arrow will typically be reading 40+ kts because acceleration rates are usually very high. The same is the case for landing, where the trend arrow will be typically indicating very high deceleration rates - 40+ kts again.
On a rejected takeoff, the Airbus AOM SOP requirement is to "observe or apply maximum braking". That means feeling the shoulder straps locked (because the deceleration rate is so high) and observing the trend arrow is off-scale in the deceleration range. One concludes from this, that observing the green deceleration light alone is not an adequate observation of deceleration performance in high-demand circumstances.
When the autobrake system is armed (LO or MED for landing, MAX for takeoff), the green deceleration light in the arming switch is an indication of the raw deceleration rate which is being achieved by the combination of both the engine thrust reversers and the autobrake system.
In other words, the higher the reverse thrust used when decelerating, the less the brakes are "contributing" to the overall deceleration rate. With no reverse thrust being used or available, the green light indication would still work providing the autobrakes were armed, and would still indicate green if the programmed deceleration rate was being achieved by brakes alone.
In other words, the green light indication "doesn't care" which system is "contributing" to the deceleration rate so long as the programmed rate (see below) is being achieved. The "Note" in the AOM says, on slippery runways, the deceleration rate may not be achieved due to brake-release by the anti-skid system. In this case, the green decel light will not come on. What is not explained or discussed is, with sufficient reverse thrust, would the deceleration light come on? The book does not say. In all cases however, the speed trend arrow is the most reliable, immediate indication of deceleration rate.
For interested non-pilots: Besides, reverse thrust is seen at best as "blocking forward thrust" rather than actually providing a significant forward thrust vector. Remember, there is still a positive thrust component from the engine through the exhaust tailpipe - it is only the huge airflow from the N1 fan that is deflected slightly forward.
Sl4yer's comment above is appropos here.
*AUTO/BRK panel
The springloaded MAX, MED, and LO pushbutton switches arm the appropriate deceleration rate.
The springloaded MAX, MED, and LO pushbutton switches arm the appropriate deceleration rate.
–
MAX mode is normally selected for takeoff.
If the pilot aborts the takeoff, maximum pressure goes to the brakes as soon as the system
generates the ground spoiler deployment order.
–
generates the ground spoiler deployment order.
–
MED or LO mode is normally selected for landing.
•
LO mode sends progressive pressure to the brakes 4 seconds after the ground spoilers deploy
in order to decelerate the aircraft at 1.7 meters/second2 (5.6 feet/second2).
•
•
MED mode sends progressive pressure to the brakes 2 seconds after the ground spoilers deploy
in order to decelerate the aircraft at 3 meters/second2 (9.8 feet/second2).
–
–
Lights :
•
The blue ON light comes on to indicate positive arming.
•
The green DECEL light comes on when the actual deceleration is 80% of the selected rate.
Note:
On slippery runway, the predetermined deceleration may not be reached due to antiskid
operation. In this case DECEL light will not illuminate. This does not mean that autobrake
is not working.
is not working.
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There is certainly a definite retarding force from the 737 reversers, PJ, which you will sense when you cancel them. However, the braking action reversers provide will be nowhere near the 'target' for the brake setting so I cannot see how the AB light would illuminate if the brakes were ineffective.
I am still wrestling with the fact that (apparently reliably) the a/c impacted the building at 94kts? The a/c would certainly have been travelling at 94kts+ as it reached the end of the runway at CGH. I don't know a MLM Vref for the 320, but let's assume 140kts? Let's also give the crew a 'fair go' and say they touched down 1000' in at Vref. 5000' later they have only lost around 40kts? Drag and rolling resistance, even without a single reverser, would surely do better? There HAS to be significant forward thrust there somewhere.
When do we expect an interim report?
I am still wrestling with the fact that (apparently reliably) the a/c impacted the building at 94kts? The a/c would certainly have been travelling at 94kts+ as it reached the end of the runway at CGH. I don't know a MLM Vref for the 320, but let's assume 140kts? Let's also give the crew a 'fair go' and say they touched down 1000' in at Vref. 5000' later they have only lost around 40kts? Drag and rolling resistance, even without a single reverser, would surely do better? There HAS to be significant forward thrust there somewhere.
When do we expect an interim report?
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I am still wrestling with the fact that (apparently reliably) the a/c impacted the building at 94kts? The a/c would certainly have been travelling at 94kts+ as it reached the end of the runway at CGH. I don't know a MLM Vref for the 320, but let's assume 140kts? Let's also give the crew a 'fair go' and say they touched down 1000' in at Vref. 5000' later they have only lost around 40kts? Drag and rolling resistance, even without a single reverser, would surely do better? There HAS to be significant forward thrust there somewhere
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Interim reports are due within 30 days after the occurrence according to ICAO Annex 13, if I remember rightly. However, Annex 13 also says things about not commencing legal proceedings until after the causal investigation is complete, and Brazil has not held to that with respect to the Amazonian midair collision, so it is not clear that they will necessarily hold to the 30-day interim-report requirement.
However, the NTSB is reading the recorders. If there is a significant safety issue with regard to airplane systems, or their operation, that the NTSB feels needs to be brought to the attention of operators immediately, they will issue a safety recommendation on their own timetable, which means as soon as they have identified the issue. (As they did with the "TCAS INOP" annunciation on the flight display as a consequence of the midair.) They have not yet done that, and I understand the recorders have largely, or completely, been read. It is reasonable to assume the NTSB has not identified any immediate safety-of-flight issue that has to do with the AC or its general operation. Either that, or it is complex enough that no one understands it yet. But in that case, I would expect them to issue a safety recommendation that restricts operation of the affected system to within certain clearly-safe parameters. They haven't done that either.
This is a bit like reading tea-leaves. But again, if you don't see tea-leaves lying on the bottom right of the cup, you can infer it wasn't tilted to the right.
Brazilian authorities have already commented that the speed on touchdown was "within parameters" (if I remember correctly), as well as that it hit the building at a certain precise speed, so one could hope that, having partial released the landing parameters they would see fit to publish all of them in the interim report by 16 August.
PBL
However, the NTSB is reading the recorders. If there is a significant safety issue with regard to airplane systems, or their operation, that the NTSB feels needs to be brought to the attention of operators immediately, they will issue a safety recommendation on their own timetable, which means as soon as they have identified the issue. (As they did with the "TCAS INOP" annunciation on the flight display as a consequence of the midair.) They have not yet done that, and I understand the recorders have largely, or completely, been read. It is reasonable to assume the NTSB has not identified any immediate safety-of-flight issue that has to do with the AC or its general operation. Either that, or it is complex enough that no one understands it yet. But in that case, I would expect them to issue a safety recommendation that restricts operation of the affected system to within certain clearly-safe parameters. They haven't done that either.
This is a bit like reading tea-leaves. But again, if you don't see tea-leaves lying on the bottom right of the cup, you can infer it wasn't tilted to the right.
Brazilian authorities have already commented that the speed on touchdown was "within parameters" (if I remember correctly), as well as that it hit the building at a certain precise speed, so one could hope that, having partial released the landing parameters they would see fit to publish all of them in the interim report by 16 August.
PBL
Hand Solo # 619“MAX autobrake is used for RTOs not regular landings. If you use it you are quite likely to cook your brakes and the aircraft won't be going anywhere in a hurry.”
This is a very short sighted and inappropriate view.
MAX is used for takeoff. Also, when landing in contaminated conditions most aircraft manufacturers require MAX as the normal procedure.
As discussed in this thread, wet runways are not all the same or have the same standard of overrun area, thus pilots (operator) are required to exercise judgement to maintain a high level of safety; this often requires a high level of braking. In these situations it is your judgement that decides that the balance between safety and commerce has to be biased even further towards safety.
Brake temps are not an issue; whilst you might ‘cook’ the brakes on a max energy RTO, landing within published weights and using max braking is well within the certified limits of all aircraft.
Instead of thinking about not being able to taxi due to brake issues, consider not being able to move because you have gone of the end!
Brake for safety not for comfort or economics.
This is a very short sighted and inappropriate view.
MAX is used for takeoff. Also, when landing in contaminated conditions most aircraft manufacturers require MAX as the normal procedure.
As discussed in this thread, wet runways are not all the same or have the same standard of overrun area, thus pilots (operator) are required to exercise judgement to maintain a high level of safety; this often requires a high level of braking. In these situations it is your judgement that decides that the balance between safety and commerce has to be biased even further towards safety.
Brake temps are not an issue; whilst you might ‘cook’ the brakes on a max energy RTO, landing within published weights and using max braking is well within the certified limits of all aircraft.
Instead of thinking about not being able to taxi due to brake issues, consider not being able to move because you have gone of the end!
Brake for safety not for comfort or economics.
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Also, when landing in contaminated conditions most aircraft manufacturers require MAX as the normal procedure
Max is Max! It is an RTO only setting, and Airbus are clear that it is not recommended for landing. It is basically brakes fully on, only limited by Anti-Skid. It would be extremely uncomfortable for passengers...
At short airfields, the brake setting you use is pretty irrelevant. The landing technique and surface condition are far more important.
I seem to recall the 757/767 has 1-5 Autobrake and an RTO ? setting? Max in an Airbus equates to RTO in a Boeing, and I doubt it is ever recommneded (or even possible?) to select RTO in a Boeing for landing...
PBL:
Just a point of clarification to your posting. The investigation is the responsiblity of the Brazilian authorities. The NTSB is an interested party, and they are providing a service to the Brazilian authorities by downloading and interpreting the CVR / FDR. The NTSB are not the investigating authority, and as such, they cannot issue interim recommendations unless they have permission from the investigating authority, similar to how Airbus had permission from Brazil to issue their AIT earlier this week.
Just a point of clarification to your posting. The investigation is the responsiblity of the Brazilian authorities. The NTSB is an interested party, and they are providing a service to the Brazilian authorities by downloading and interpreting the CVR / FDR. The NTSB are not the investigating authority, and as such, they cannot issue interim recommendations unless they have permission from the investigating authority, similar to how Airbus had permission from Brazil to issue their AIT earlier this week.
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A320 autobrake
Originally Posted by PEI_3721
MAX is used for takeoff. Also, when landing in contaminated conditions most aircraft manufacturers require MAX as the normal procedure.
As has been discussed here, there are three autobrake settings on the A320, LO, MED and MAX.
LO has a target deceleration of 1.7m/s/s, MED of 3.0 m/s/s, and MAX has no such limit and brakes as hard as possible. MAX is only to be used for rejected take-offs.
On slippery surfaces (and I'm not implying anything about the state of the accident runway), 3m/s/s may not be achievable at all, so MED and MAX settings will have the same effect.
If not even 1.7m/s/s can be achieved, LO will provide the same deceleration, but LO autobrake starts 2 seconds later than MED (4s after ground spoiler deployment, vs. 2s in MED), so the total distance will be longer.
This also makes it clear that the thrust reversers do not shorten the braking distance when the friction between wheels and runway can achieve 3m/s/s (or 1.7m/s/s for "LO" autobrake). They just ease some of the strains on the brakes.
To convey that "MAX" is different from LO and MED, its pushbutton is set slightly separated from the other two.
Just getting the physics and autobrake logic straight.
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Congratulations
First, congratulations to all members of this forum, specially in this thread. I´m only a reader and entusiast from Brazil (sorry my bad english). I need to put a question publish today in brazilian media - Revista Veja and I use a Babelfish translator (some erros in automatic translate). For Yours opinions:
MAGAZINE VEJA: GUILT WAS OF THE PILOT
A human error is in the origin of the worse air accident of the history of Brazilian aviation. The information already gotten by means of the analysis of the box-black color of the Airbus A320 of the TAM – that in last day 17 if the death of 199 people shocked against a building of the company, causing – they indicate that the airplane, when settling, did not obtain to decelerate the sufficient because of an error of the commander of the flight.
These information, still kept in secrecy for the commission of the Aeronautics that investigates the accident, show that one of the two handspikes that regulate the functioning of the turbines, called manetes, was is of position when the airplane touched down main of the Airport of Congonhas. The error made with that the turbines of the Airbus functioned in opposing directions: while the left helped the airplane to brake, as he was desired, the right made it to speed up.
With this, the airplane, that settled about 240 kilometers for the moment, did not obtain to stop. Inquiries still disclose that, despite rain, it did not have aquaplaning in the track nor fails in the system of brakes of the tires. The news article of SEES also selected that who piloted the Airbus at the moment of the accident was Kleyber commander Rasp, and not, as suspected the Aeronautics, the copilot Enrique Stephanini Di Sacco, that is dismissed of the Goal after three months of work and was in the TAM had little time.
The complete inquiry of the accident will have to still last ten months. However, already it was arrived at the conclusion of that the error of the pilot was same the initial cause of the accident – that, it was not for the characteristics of the track of the Airport of Congonhas, could have had very lesser consequences. The reasons that had led to the fall of the Airbus of the TAM have indirect relation with the fact of the aircraft to be flying in that day with the stopped right reverse.
Reverse is a mechanism that, when inverting the air flow of the turbines, helps to decelerate the airplane. As the system of lockwire of an aircraft he is composed of a set of resources, a device can even fly without problems with one of the disactivated reverses or with two. Only that, when this happens, the pilot, when settling, has to operate manetes of different form of the routine. E this is what it can have confused the commander of the flight.
When keeping manete of the right turbine – that he was with the stopped reverse – in acceleration position, and not in the position "idling", it hindered the complete lockwire it airplane, that for the moment crossed the end of the track to a next speed the 200 kilometers. One is not about an unknown error. It was committed by the pilots of the o but others two aircraft of the same model, the A320 of the Airbus. As much in the disaster occurred in March of 1998, in the Phillipino, how much in the accident that had in 2004, in the airport of Taipei, in Taiwan, one concluded that he had imperfections in the operation of manetes.
The coincidences go beyond: in the two cases, the airplanes were with one of the stopped turbines, accurately as in the accident of the TAM. In the Phillipino, a flight of the Airlines Phillipine passed direct for the track and alone it after stopped shocking itself with barracos wooden in the neighborhoods. In 2004, the fact if repeated with rigorous exactness. Of this time, a A320 crossed the track of the airport of Taipei. Again the inquiries had shown that manete of the turbine that had the stopped reverse it was in the missed position, pushing the onward A320.
In the thursday, Brigadier General Jorge Kersul Son, head of the inquiries of the Center of Inquiry and Prevention of Aeronautical Accidents (Cenipa) of the Ministry of the Defense, said that the landing with the stopped reverse can have psicologicamente "influenced" the pilots. He still said to be improbable that the absence of grooves for water draining in Congonhas, grooving, has had some relation with the accident (it rained in São Paulo in the night of day 17).
The conclusion is that it did not have aquaplaning in the day of the tragedy. Apóia it in three evidences. The first one of them is the absence of specific marks in the track of the airport. These marks are formed when the water under the tires of an aircraft that is skidding esquenta until the boil point. They are clear, very different of the black marks caused by normal lockwires. In the track of Congonhas, such marks had not been found. The data already harvested in the box-black color and the analysis of that it remained of the tires of the Airbus, found in rubbles of the building of the TAM, had moved away from time this hypothesis. (Source: Magazine VEJA)
The original in brazilian portuguese can read here
MAGAZINE VEJA: GUILT WAS OF THE PILOT
A human error is in the origin of the worse air accident of the history of Brazilian aviation. The information already gotten by means of the analysis of the box-black color of the Airbus A320 of the TAM – that in last day 17 if the death of 199 people shocked against a building of the company, causing – they indicate that the airplane, when settling, did not obtain to decelerate the sufficient because of an error of the commander of the flight.
These information, still kept in secrecy for the commission of the Aeronautics that investigates the accident, show that one of the two handspikes that regulate the functioning of the turbines, called manetes, was is of position when the airplane touched down main of the Airport of Congonhas. The error made with that the turbines of the Airbus functioned in opposing directions: while the left helped the airplane to brake, as he was desired, the right made it to speed up.
With this, the airplane, that settled about 240 kilometers for the moment, did not obtain to stop. Inquiries still disclose that, despite rain, it did not have aquaplaning in the track nor fails in the system of brakes of the tires. The news article of SEES also selected that who piloted the Airbus at the moment of the accident was Kleyber commander Rasp, and not, as suspected the Aeronautics, the copilot Enrique Stephanini Di Sacco, that is dismissed of the Goal after three months of work and was in the TAM had little time.
The complete inquiry of the accident will have to still last ten months. However, already it was arrived at the conclusion of that the error of the pilot was same the initial cause of the accident – that, it was not for the characteristics of the track of the Airport of Congonhas, could have had very lesser consequences. The reasons that had led to the fall of the Airbus of the TAM have indirect relation with the fact of the aircraft to be flying in that day with the stopped right reverse.
Reverse is a mechanism that, when inverting the air flow of the turbines, helps to decelerate the airplane. As the system of lockwire of an aircraft he is composed of a set of resources, a device can even fly without problems with one of the disactivated reverses or with two. Only that, when this happens, the pilot, when settling, has to operate manetes of different form of the routine. E this is what it can have confused the commander of the flight.
When keeping manete of the right turbine – that he was with the stopped reverse – in acceleration position, and not in the position "idling", it hindered the complete lockwire it airplane, that for the moment crossed the end of the track to a next speed the 200 kilometers. One is not about an unknown error. It was committed by the pilots of the o but others two aircraft of the same model, the A320 of the Airbus. As much in the disaster occurred in March of 1998, in the Phillipino, how much in the accident that had in 2004, in the airport of Taipei, in Taiwan, one concluded that he had imperfections in the operation of manetes.
The coincidences go beyond: in the two cases, the airplanes were with one of the stopped turbines, accurately as in the accident of the TAM. In the Phillipino, a flight of the Airlines Phillipine passed direct for the track and alone it after stopped shocking itself with barracos wooden in the neighborhoods. In 2004, the fact if repeated with rigorous exactness. Of this time, a A320 crossed the track of the airport of Taipei. Again the inquiries had shown that manete of the turbine that had the stopped reverse it was in the missed position, pushing the onward A320.
In the thursday, Brigadier General Jorge Kersul Son, head of the inquiries of the Center of Inquiry and Prevention of Aeronautical Accidents (Cenipa) of the Ministry of the Defense, said that the landing with the stopped reverse can have psicologicamente "influenced" the pilots. He still said to be improbable that the absence of grooves for water draining in Congonhas, grooving, has had some relation with the accident (it rained in São Paulo in the night of day 17).
The conclusion is that it did not have aquaplaning in the day of the tragedy. Apóia it in three evidences. The first one of them is the absence of specific marks in the track of the airport. These marks are formed when the water under the tires of an aircraft that is skidding esquenta until the boil point. They are clear, very different of the black marks caused by normal lockwires. In the track of Congonhas, such marks had not been found. The data already harvested in the box-black color and the analysis of that it remained of the tires of the Airbus, found in rubbles of the building of the TAM, had moved away from time this hypothesis. (Source: Magazine VEJA)
The original in brazilian portuguese can read here
Last edited by spyk; 28th Jul 2007 at 21:45.
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From FCOM 01.32.30
"MAX autobrake mode cannot be armed in flight."
From FCTM 02.160.07 (Chapter is discussing landing brake techniques and auto brake use at landings.)
"The use of MAX autobrake is not recommended"
"MAX autobrake mode cannot be armed in flight."
From FCTM 02.160.07 (Chapter is discussing landing brake techniques and auto brake use at landings.)
"The use of MAX autobrake is not recommended"
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Originally Posted by PEI_3721
I agree with Nigel and bsieker you couldn't have explained better.
For the A320 Airbus clearly states :
Autobrake mode in SOP :
LO setting for long and dry runways;
MED for short or contaminated runways;
MAX not recommended for landing
PS : Of course agree with Rippa too, você foi mais rapido.
MAX is used for takeoff. Also, when landing in contaminated conditions most aircraft manufacturers require MAX as the normal procedure.
For the A320 Airbus clearly states :
Autobrake mode in SOP :
LO setting for long and dry runways;
MED for short or contaminated runways;
MAX not recommended for landing
PS : Of course agree with Rippa too, você foi mais rapido.
Last edited by Config Full; 28th Jul 2007 at 21:17. Reason: Added PS
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inop thrust rev. fwd thrust
With 1 inop reverser and you pull full reverse on both reversers.
" When keeping manete of the right turbine – that he was with the stopped reverse – in acceleration position, and not in the position "idling", it hindered the complete lockwire it airplane, that for the moment crossed the end of the track to a next speed the 200 kilometers."
Don't quite understand the translation, anyone got more info on this ?
inop rewas lockwired ?
You would have forward thrust on the engine with the inop reverser which would increase groundspeed and contribute to an aircraft going off the side.
There's a caution in the MEL on this in regards to inop reverser.
Forgive me if this is previously posted ( have not been able to read all the posts )
" When keeping manete of the right turbine – that he was with the stopped reverse – in acceleration position, and not in the position "idling", it hindered the complete lockwire it airplane, that for the moment crossed the end of the track to a next speed the 200 kilometers."
Don't quite understand the translation, anyone got more info on this ?
inop rewas lockwired ?
You would have forward thrust on the engine with the inop reverser which would increase groundspeed and contribute to an aircraft going off the side.
There's a caution in the MEL on this in regards to inop reverser.
Forgive me if this is previously posted ( have not been able to read all the posts )
Last edited by Mach trim; 28th Jul 2007 at 21:58.
Altough the automatic translation is barely readable the VEJA article sums it pretty well I'm afraid 
Interesting one... first time I hear it. Anyone with further info on this topic (specific and distinct tire marks for aquaplaning aircrafts) ?
The first one of them is the absence of specific marks in the track of the airport. These marks are formed when the water under the tires of an aircraft that is skidding esquenta until the boil point. They are clear, very different of the black marks caused by normal lockwires.
MAX Braking.
A point which is perhaps being overlooked it that on those runways where the conditions are such that the normal braking performance may not be achieved, then the maximum level of braking (brakes + reverse) will not result in uncomfortable deceleration. MAX (or RTO) is attempting to achieve a very high level of retardation, but due to anti skid action or aquaplane etc, this is not being achieved. Aspects of this are in the presentation - Boeing slippery runways.
The deceleration during landing depends primarily on the runway friction, which is a function of materials, construction, and ‘contaminant’ – wet, dust, etc (not necessarily contaminated). The discussion should not get hung up with auto brake of definitions as it is the level of braking required / achieved that is important. It easier to understand that ‘feet on the floor’ is maximum braking requested, this is the best situation if the achieved braking is poor, and particularly if the runway conditions vary – water patches, as the best retardation is immediately available.
The point on safety margins has been discussed in other threads on runway braking conditions. The significant points are that although the certificated landing distances involve a factored distance, the resultant safety margins are not the same. We often equate a wet landing with a distance factor of 1.92 as having a safety margin of .92 (not an exact science), but in standing water (up to 3mm) the safety margins are much smaller and in some circumstances (combinations of conditions such as wet and non grooved) the margin might be nil, thus maximum braking is required throughout the landing, just in case.
Some of these issues are in UK AIC 11/98 P164 and 3/2007 P111, but these, as with some certification aspects do not give all of the assumptions or conditions; a most important one is that the unfactored landing performance is based on maximum braking (on a dry runway) and that all other aspects are calculated – factored with more assumptions.
Checking the other threads will indicate that in extreme circumstances (snow / ice contamination), even a landing with a factored distance of 2.4 may only just maintain the safety margins that we are all familiar with in daily operations. One of the references from NASA shows that a wet, non grooved runway has similar fiction characteristics to that of loose snow or thin ice!
Ignore the auto brake aspects – concentrate on stopping; PEI’s point would be better presented by stating - use ‘Maximum Braking’ in adverse conditions.
The deceleration during landing depends primarily on the runway friction, which is a function of materials, construction, and ‘contaminant’ – wet, dust, etc (not necessarily contaminated). The discussion should not get hung up with auto brake of definitions as it is the level of braking required / achieved that is important. It easier to understand that ‘feet on the floor’ is maximum braking requested, this is the best situation if the achieved braking is poor, and particularly if the runway conditions vary – water patches, as the best retardation is immediately available.
The point on safety margins has been discussed in other threads on runway braking conditions. The significant points are that although the certificated landing distances involve a factored distance, the resultant safety margins are not the same. We often equate a wet landing with a distance factor of 1.92 as having a safety margin of .92 (not an exact science), but in standing water (up to 3mm) the safety margins are much smaller and in some circumstances (combinations of conditions such as wet and non grooved) the margin might be nil, thus maximum braking is required throughout the landing, just in case.
Some of these issues are in UK AIC 11/98 P164 and 3/2007 P111, but these, as with some certification aspects do not give all of the assumptions or conditions; a most important one is that the unfactored landing performance is based on maximum braking (on a dry runway) and that all other aspects are calculated – factored with more assumptions.
Checking the other threads will indicate that in extreme circumstances (snow / ice contamination), even a landing with a factored distance of 2.4 may only just maintain the safety margins that we are all familiar with in daily operations. One of the references from NASA shows that a wet, non grooved runway has similar fiction characteristics to that of loose snow or thin ice!
Ignore the auto brake aspects – concentrate on stopping; PEI’s point would be better presented by stating - use ‘Maximum Braking’ in adverse conditions.