Manual braking
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Manual braking
737 FCTM says:
"Manual Braking
Immediately after main gear touchdown, smoothly apply constant brake pedal pressure for the desired braking. For short or slippery runways, use full brake pedal pressure."
that's fine, but on another page it says:
"Although immediate braking is desired, manual braking techniques normally invovle a four to five second delay between main gear touchdown and brake pedal application even when actual conditions reflects the need for a more rapid initiation of braking. This delayed braking can result in the loss of 800 to 1,000 feet of runway..."
Now I'm confused which one should I follow? should I wait 4/5 seconds after MLG touchdown for brake application? or should I immediately apply brakes after MLG touchdown (without the 4/5 seconds delay) and perhaps the antiskid itself will do the delay in order to prevent 'locked wheel during touch down'?
thanks in advance
"Manual Braking
Immediately after main gear touchdown, smoothly apply constant brake pedal pressure for the desired braking. For short or slippery runways, use full brake pedal pressure."
that's fine, but on another page it says:
"Although immediate braking is desired, manual braking techniques normally invovle a four to five second delay between main gear touchdown and brake pedal application even when actual conditions reflects the need for a more rapid initiation of braking. This delayed braking can result in the loss of 800 to 1,000 feet of runway..."
Now I'm confused which one should I follow? should I wait 4/5 seconds after MLG touchdown for brake application? or should I immediately apply brakes after MLG touchdown (without the 4/5 seconds delay) and perhaps the antiskid itself will do the delay in order to prevent 'locked wheel during touch down'?
thanks in advance
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the delay usually refers to the fact that you have to move your feet from "heels on the floor" to a position on the pedals where you can apply brakes.
Often one needs to keep the aircraft straight with rudder and it takes a couple of seconds to move your feet, also, if you apply manual braking immediately on touchdown it may cause the Nose gear to slam onto the runway, whereas if you have selected "autobrake" the braking process commences faster and probably smoother.
Hope that helps.
Often one needs to keep the aircraft straight with rudder and it takes a couple of seconds to move your feet, also, if you apply manual braking immediately on touchdown it may cause the Nose gear to slam onto the runway, whereas if you have selected "autobrake" the braking process commences faster and probably smoother.
Hope that helps.
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"the delay usually refers to the fact that you have to move your feet from "heels on the floor" to a position on the pedals where you can apply brakes"
Well, thanks. I didn't really thought about that!
"also, if you apply manual braking immediately on touchdown it may cause the Nose gear to slam onto the runway"
I guess this will not happens as long as I apply manual brakes 'smoothly' and 'constant' as the FCTM said. Unless the antiskid in inoperative:
"When the antiskid system is inoperative, the following techniques apply:
- ensure that the nose wheels are on the ground and the speedbrakes are extended before applying the brakes.
- initiate wheel braking using very light pedal pressure and increase pressure as ground speed decreases
- apply steady pressure and DO NOT PUMP the pedal"
Well, thanks. I didn't really thought about that!
"also, if you apply manual braking immediately on touchdown it may cause the Nose gear to slam onto the runway"
I guess this will not happens as long as I apply manual brakes 'smoothly' and 'constant' as the FCTM said. Unless the antiskid in inoperative:
"When the antiskid system is inoperative, the following techniques apply:
- ensure that the nose wheels are on the ground and the speedbrakes are extended before applying the brakes.
- initiate wheel braking using very light pedal pressure and increase pressure as ground speed decreases
- apply steady pressure and DO NOT PUMP the pedal"
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Don’t be confused, it is a matter of applied airmanship. Braking should be commensurative with required stopping distance, current conditions and planned runway exit point.
Landing on a 10,000 ft runway, applying maximum brakes on touchdown and clearing by the first taxi-way only results in the brake temps in the red zone and does nothing for passenger comfort or your company’s bottom line. A touch of brakes as you cancel the reverse thrust would be more than enough.
Then again minimum brakes on a contaminated 6000 ft runway could also produce a detrimental result.
Evaluate the conditions prior to landing and make the appropriate response.
Landing on a 10,000 ft runway, applying maximum brakes on touchdown and clearing by the first taxi-way only results in the brake temps in the red zone and does nothing for passenger comfort or your company’s bottom line. A touch of brakes as you cancel the reverse thrust would be more than enough.
Then again minimum brakes on a contaminated 6000 ft runway could also produce a detrimental result.
Evaluate the conditions prior to landing and make the appropriate response.
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wof - there should be no confusion.
Para 1: "Manual Braking Immediately after main gear touchdown," etc etc is simply a statement of how Boeing say you should do it.
Para 2: "Although immediate braking is desired, manual braking techniques normally...." etc etc is simply advising you of what tends to happen (refer flufdriver) and the effect of that.
Follow the book (or, of course, your company Ops Manual if different).
Para 2 is also an indication of why autobrake is a better option if distances are near limiting.
Para 1: "Manual Braking Immediately after main gear touchdown," etc etc is simply a statement of how Boeing say you should do it.
Para 2: "Although immediate braking is desired, manual braking techniques normally...." etc etc is simply advising you of what tends to happen (refer flufdriver) and the effect of that.
Follow the book (or, of course, your company Ops Manual if different).
Para 2 is also an indication of why autobrake is a better option if distances are near limiting.
Read the FCTM very carefully when it comes to braking (autobrake or manual brake) if landing in a crosswind on a slippery runway. Among other things it cautions on having a directional control problem during the roll-out on a slippery runway. The relevant diagram in the FCTM says it all.
The Boeing 737 advice is to release the brakes and reduce reverse thrust to reverse idle. When directional control is regained and the aircraft is correcting towards the runway centre-line, apply maximum braking and symmetrical reverse thrust to stop the aircraft.
If landing on a slippery runway then most pilots would use an appropriate autobrake setting. Perhaps even max. They would probably use max reverse thrust for effective stopping since the brakes would not be as effective as on a dry surface. If the aircraft starts sliding sideways, then consider how the pilot should release the brakes completely. Pedal pressure increase or switch the autobrake selector to off? Either way, whatever you do, don't cancel the autobrakes by placing the speed brake lever down!
Next move is to reduce to idle reverse. Try that next time in the simulator and note how long it takes to go from max reverse N1 of around 90 percent, to idle reverse of 23 percent. I'll tell you. It takes at least 10 seconds and more. And if you stuff up and quickly place the reverse levers right down to what you fondly hope is reverse idle, the engine will be still delivering around 60 percent N1 forward thrust as the reverser lights extinguish. The last thing you need is all that forward thrust on a slippery runway...
Continue to follow the FCTM advice and try and get the aircraft straight by using rudder and judicious use of brake. Good. Got the aircraft straight by now? That takes a few seconds with no braking going on except for the speed brake drag. By now you have used an alarming amount of runway. Now apply max braking again and full reverse if needed.
Did you know it takes at least 10 seconds to spool up from idle reverse of 23 percent N1 to 90 percent N1 full reverse. In fact, that is why on touch down the N1 stays at 31 percent N1 until four seconds after touch down and if reverse has not been selected by then, the N1 falls back to 23 percent to reduce excess thrust and thus landing run distance.
Sounds too complicated? Well it is - and if landing on a slippery runway in a significant crosswind, you need to know exactly what you are doing in terms of FCTM techique and why. So your questions on manual or autobraking, heels on the floor or up on the brakes, and what if anti-skid is u/s, are all pertinent.
They fade in importance however, when you consider the fancy footwork and reverse thrust fiddling needed to handle a slide sideways caused by weather- cocking and reverse thrust vectors. It sorts the men from the boys.
The Boeing 737 advice is to release the brakes and reduce reverse thrust to reverse idle. When directional control is regained and the aircraft is correcting towards the runway centre-line, apply maximum braking and symmetrical reverse thrust to stop the aircraft.
If landing on a slippery runway then most pilots would use an appropriate autobrake setting. Perhaps even max. They would probably use max reverse thrust for effective stopping since the brakes would not be as effective as on a dry surface. If the aircraft starts sliding sideways, then consider how the pilot should release the brakes completely. Pedal pressure increase or switch the autobrake selector to off? Either way, whatever you do, don't cancel the autobrakes by placing the speed brake lever down!
Next move is to reduce to idle reverse. Try that next time in the simulator and note how long it takes to go from max reverse N1 of around 90 percent, to idle reverse of 23 percent. I'll tell you. It takes at least 10 seconds and more. And if you stuff up and quickly place the reverse levers right down to what you fondly hope is reverse idle, the engine will be still delivering around 60 percent N1 forward thrust as the reverser lights extinguish. The last thing you need is all that forward thrust on a slippery runway...
Continue to follow the FCTM advice and try and get the aircraft straight by using rudder and judicious use of brake. Good. Got the aircraft straight by now? That takes a few seconds with no braking going on except for the speed brake drag. By now you have used an alarming amount of runway. Now apply max braking again and full reverse if needed.
Did you know it takes at least 10 seconds to spool up from idle reverse of 23 percent N1 to 90 percent N1 full reverse. In fact, that is why on touch down the N1 stays at 31 percent N1 until four seconds after touch down and if reverse has not been selected by then, the N1 falls back to 23 percent to reduce excess thrust and thus landing run distance.
Sounds too complicated? Well it is - and if landing on a slippery runway in a significant crosswind, you need to know exactly what you are doing in terms of FCTM techique and why. So your questions on manual or autobraking, heels on the floor or up on the brakes, and what if anti-skid is u/s, are all pertinent.
They fade in importance however, when you consider the fancy footwork and reverse thrust fiddling needed to handle a slide sideways caused by weather- cocking and reverse thrust vectors. It sorts the men from the boys.
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To cancel A/B as you are drifting on a windy contaminated runway,DO NOT SWICTH OFF the A/B manually but use Manual braking.
90% N1 reverse...must be a hell of a short and contaminated runway...
90% N1 reverse...must be a hell of a short and contaminated runway...
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To cancel A/B as you are drifting on a windy contaminated runway,DO NOT SWICTH OFF the A/B manually but use Manual braking.
90% N1 reverse...must be a hell of a short and contaminated runway...
90% N1 reverse...must be a hell of a short and contaminated runway...
The FCTM states the brakes should be released if the aircraft starts drifting sideways on a slippery runway. By applying manual brakes to disarm the autobrakes you are momentarily applying more brake pressure which contradicts the requirement to release the brakes. There can also be a period where the pilot is unsure if indeed he has applied sufficient foot pressure to disarm the autobrakes. A close eye on the autobrake disarmed light is vital to confirm that the disarming has taken place.
The main thing is to get the autobrakes disarmed promptly and of all the choices under the circumstances it would be logical to use the autobrake selector to the Off position.
Braking efficiency may be greatly reduced on a slippery runway, leaving only the spoilers and reverse thrust to do their work in reducing the landing roll distance. Reverse in particular is more efficient if used at high speed which means immediately on touch down. See FCTM under heading of Reverse Thrust operation. It states: "Maintain reverse thrust as required, up to the maximum, until the airspeed approaches 60 knots".
On a slippery performance limiting runway it is good airmanship to use full reverse thrust until you know for sure the aircraft will safely stop considering the reduced braking efficiency associated with slippery surfaces
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TEE EMM,
Sorry but i agree to disagree.
In a situation where you are drifting,possibly in a weathervane,deselecting the brakes by Switching the autobrake to the OFF position will dramatically increase your landing distance as your deceleration will be stopped abruptly and possibly end up in an even more unstable position.(aircraft closer to runway edge moving faster).
Also,Boeing has had issues when the A/B was selected manually to OFF,the switch triggered an RTO deceleration!...
Applying slightly and momentarily more brake pressure to release them allows you to maintain better control of your aircraft while releasing the brakes gently with minimum of distance loss.
This technique was preferred to a Boeing company 737 Instructor pilot i talked a few years back when i popped him this question.
He agreed with the manual release of brakes.
Obviously as you do so, glance at the disarm light as we always do during this braking transition, the PNF is also there to annunciate the light as you call for manual braking.
Sorry but i agree to disagree.
In a situation where you are drifting,possibly in a weathervane,deselecting the brakes by Switching the autobrake to the OFF position will dramatically increase your landing distance as your deceleration will be stopped abruptly and possibly end up in an even more unstable position.(aircraft closer to runway edge moving faster).
Also,Boeing has had issues when the A/B was selected manually to OFF,the switch triggered an RTO deceleration!...
Applying slightly and momentarily more brake pressure to release them allows you to maintain better control of your aircraft while releasing the brakes gently with minimum of distance loss.
This technique was preferred to a Boeing company 737 Instructor pilot i talked a few years back when i popped him this question.
He agreed with the manual release of brakes.
Obviously as you do so, glance at the disarm light as we always do during this braking transition, the PNF is also there to annunciate the light as you call for manual braking.
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Also,Boeing has had issues when the A/B was selected manually to OFF,the switch triggered an RTO deceleration!...
Re inadvertently going say from autobrake max right through the off position into RTO.
Like just about every other switch selection it may have unintended consequences if you stuff it up. Until a recent Boeing 737 revision, after landing the autobrake switch position was not changed for the reason you mentioned. The switch was placed to autobrake off during the shut down scans.
I believe that has been changed so that the autobrake selector is now switched off during the after landing scans. I sometimes wish Boeing would not fart around with checklist items unless absolutely necessary. One of the diagrams in the FCTM shows a visual circuit pattern. It used to be 1.5 miles wide. Then Boeing changed it to 2 miles wide "to standardise with other Boeing models". I cannot see the logic of that statement. For 33 years the 1.5 mile wide circuit was ideal. Suddenly it isn't anymore. Huh?
For my part one of the worst changes that Boeing made with the 737 checklists was the after take off check. Among other items in the old days it said "Air Conditioning and Pressurisation.....Set" Or maybe it was "checked". I can't remember.
Boeing changed that by deleting the wording and instead brought in a check of the positions of the bleed, isolation and pack switches. Commonsense indicates a wise pilot would also check the cabin rate of climb and differential as part of the check. But from personal observation in many sim trips the number of crew (captain and copilot) who never checked the cabin pressurisation instruments was quite worrying. Worse still, we noticed that the captain rarely looked up and across to the pressurisation panel to confirm the actions of the copilot. In other words if the item was not on the checklist it was not checked.
Now back to brakes on slippery runways.
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Call me a pedant, but you're all discussing pedal braking, not manual braking. I've used manual braking on many aircraft - memorably the DH Dove and Chipmunk, and many gliders...
