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B-HKD
12th Aug 2007, 05:00
Evening,

I have been studying the Qantas 744 SOP for a while now. As we all know it has changed since the BKK overrun, and this is good. But what has made me wondering is how it was changed.

It used to be Flaps 25 for all landings except for HKG/Kait Tak and where operations required it.

The autobrake selection was 2 as a standard and idle reverse.

Now (correct me if wrong) i have this info from a QF 744 F/O the standard has become:

Flaps 30

Autobrake 3

and Full Reverse. (except for SYD in early hours and LHR/FRA noise restricted)


I know QF wants to prevent such thing happening again but havent they changed it a little to strictly?

I mean safety goes first and the sorter the landing the safer, but Autobrakes 3 and Full reverse is a pretty quick slowdown on a 744.

I mean "Strictly" because nowadays especially brakepads and engine overhauls are very expensive.

And most other carriers have a Flaps 25/30 usual Autobrakes 2 and idle reverse in normal weather conditions.

since carbon brakes "Like" heat, idle reverse gives them more use and also saves engine wear.

Are there any QF people who could give me a idea of their daily OPS and how they really do it.

THanks in advance

Leo

jtr
12th Aug 2007, 05:19
I am not in QF (judging by your id I think I might be in the same company as you)

AB3 and idle reverse will give you more or less the same stopping dist. as AB3 and full reverse.

Operating into busy airfields and dawdling down the RWY using AB2 is not likely to get favourable commentary from the tower.

Must admit full rev is probably a bit of overkill if the rwy is long and dry, but I am sure they thought it through before they implemented it.

With my lot AB3 and idle rev. is the "standard" landing set up.

Wizofoz
12th Aug 2007, 05:35
I always felt this was something of a knee-jerk reaction to the BKK incident. The accident report went into great detail regarding the F25, idle reverse policy and aquaplaning. The facts of the case are that the aircraft touched down with NO autobrake, and neither reverse nor manual breaking were used until it was too late due to crew confusion as to who was actually flying the aircraft.

Operators I have worked for have left it up to the crews discretion where there is a choice of flap settings and we use appropriate auto-brakes to make the most expeditious exit (i.e. get the book out and have a look at the stopping distances table!).

Reduced flap/idle reverse landings have economic (especially with carbon brakes) and noise/environmental advantages. To not use them on a long, dry runway seems overly prescriptive to me.

B-HKD
12th Aug 2007, 05:52
I am not in QF (judging by your id I think I might be in the same company as you)

AB3 and idle reverse will give you more or less the same stopping dist. as AB3 and full reverse.

Operating into busy airfields and dawdling down the RWY using AB2 is not likely to get favourable commentary from the tower.

Must admit full rev is probably a bit of overkill if the rwy is long and dry, but I am sure they thought it through before they implemented it.

With my lot AB3 and idle rev. is the "standard" landing set up.

Hey, thanks for the aswer it gives me a better idea and a fully understand you :D

BTW actually I only happen to be a 15 year old aviation enthusiast that has fallen in love with the 744 :P

Thanks again

I always felt this was something of a knee-jerk reaction to the BKK incident. The accident report went into great detail regarding the F25, idle reverse policy and aquaplaning. The facts of the case are that the aircraft touched down with NO autobrake, and neither reverse nor manual breaking were used until it was too late due to crew confusion as to who was actually flying the aircraft.

Operators I have worked for have left it up to the crews discretion where there is a choice of flap settings and we use appropriate auto-brakes to make the most expeditious exit (i.e. get the book out and have a look at the stopping distances table!).

Reduced flap/idle reverse landings have economic (especially with carbon brakes) and noise/environmental advantages. To not use them on a long, dry runway seems overly prescriptive to me.

That is exactly what i was thinking. I mean ok there was an accident, but clearly thousands of landing had been made in the previouse config. and the accident was actually caused by crew errors and as you described above. So the extent of change seems a little to extremein my opinion.

BTW mind if i ask you if you work for QF?

Thanks :)

chemical alli
12th Aug 2007, 08:22
part of the ab3 concept is to enure a rapid heat builup in the carbon brakes as this stops the brakes from glazing and carbon brakes are more efficient at operating temps

Razor
12th Aug 2007, 08:55
Autobrakes 3 minimum for wet runway.
Flap 30 and Full reverse as standard
Can reduce Autobrakes and use idle reverse if runway length allows. We have Autobrake guidance data in QRH/Perf Lims manual to help with decision

chemical alli
15th Aug 2007, 01:34
just some more info ,the auto brake setting is a specefic deceleration rate so if on ab2 and full reverse maybe the equalivent to ab3 and idle reverse.

ray cosmic
15th Aug 2007, 01:41
AB3 will give you a different deceleration rate than AB2.
Rate with or without reverse should be the same per autobrake setting.
Therefore the rates still remain different. Right?

chemical alli
15th Aug 2007, 01:55
different pressure applied to brakes at different ab setting although deceleration comes into play as brakes pressure released as aircraft decelerates to maintain a constant ,therefore if reversers applied and ab selected brake pressure will be released earlier

Bolty McBolt
15th Aug 2007, 05:19
I will check my notes but if memory serves, The 744 autobrake selector scale equates directly with the pressure supplied to the brakes. eg. AB1 = 1200psi, AB2 = 1600psi, AB3 = 2000psi to RTO = 3000psi. The rotary switch could just as easily read pressure rather than 1 - 5. Perhaps this is why a greater AB selection is used on wet runways on the Boeing...
(ref AMM auto brake test)

Once the correct conditions are seen, A/C on ground, wheel spin up etc the autobrake supplies equal pressure to all brakes as dictated by the selection.
The anti-skid does the rest until the brake peddles are depressed overiding the autobrake module.


Therefore if the T/Rs are used the aircraft pulls up at a faster deceleration than without, at the same auto brake selection.

The Airbus on the other hand is a completely different story.

Spanner Turner
15th Aug 2007, 15:30
I will check my notes

Yes you’d better


OK – I shall try to set the 744 autobraking system straight!

The 744 Autobraking levels of 1, 2, 3, 4 and Max Auto are all selected levels of DECELERATION.

They equate to the following:

1 = 4.0 ft per second per second.

2 = 5.0 ft per sec/sec

3 = 6.0 ft per sec/sec

4 = 7.5 ft per sec/sec

MAX = 11.0 ft per sec/sec.

For example,

Landing speed of 130kts (219feet/sec). Autobrake “3” selected. (BSCU wants to “see” a decel of 6 ft/sec/sec)

Touchdown Speed= 130kts(219ft/sec)
after 1 secs = 126kts(213ft/sec)
after 2 secs = 122kts(207ft/sec)
after 4 secs = 115kts(195ft/sec)
after 8 secs = 101kts
after 12 secs = 87kts
after 16 secs = 72kts
after 20 secs = 58kts
after 24 secs = 44kts
after 28 secs = 30kts
after 30 secs = 23kts(39ft/sec)……… fastish taxi speed


Landing speed of 130kts (219feet/sec). Autobrake “MAX” selected. (BSCU wants to see a decel of 11 ft/sec/sec)

Touchdown Speed= 130kts(219ft/sec)
after 1 secs = 123kts(208ft/sec)
after 2 secs = 116kts(197ft/sec)
after 4 secs = 103kts(175ft/sec)
after 8 secs = 77kts
after 12 secs = 51kts
after 16 secs = 25kts (43ft/sec)………..fastish taxi speed


The Brake System Control Unit (BSCU) controls autobraking and receives aircraft deceleration data from the Inertial Reference Units.
When all arming conditions are met and the autobrakes are engaged, the BSCU will send a signal to the Autobrake Hydraulic Modules (one left and one right, located on the rear bulkhead of each wing landing gear wheel well) to port hydraulic pressure to the wheel brakes that will result in the selected deceleration rate. This signal will vary and be proportional to the amount of wheel braking required to achieve the decel rate.
i.e if you land and DO NOT select reverse and DO NOT deploy speed brakes, a greater proportion of wheel braking is required to achieve the selected decal rate. Accordingly, the BSCU will command the Autobrake Module to supply a larger amount of hydraulic press to the wheel units. The amount of hydraulic pressure supplied (and thus the actual amount of brake usage) will be increased so as to satisfy the BSCU that the aircraft is decelerating at the required rate.
Result = required decel rate but with hot brakes.

Conversely, if you land and select reverse, deploy speedbrakes, land on an upslope, land in quicksand, land and have all the passengers put their feet out on the ground or land and deploy a braking parachute(a la B52), then the amount of braking required from the wheel units to achieve the selected decel rate is reduced.
Result = required decel rate but with cooler brakes

Same as braking hard in your car. You can equate your reversers to “downshifting” in your car. If you are doing 100 km/h and shift back from 5th to 4th gear without touching the brakes or anything else, then you will slow down without using(or wearing out) your brake pads or discs.

Whilst all this is happening, the anti-skid will always override if ever needed to prevent a wheel lock-up (anti-skid operates completely autonomously).

If ever the pilot feels the need to take-over manual braking, whenever the output of either the left or right brake metering valves(i.e pilots pedals) reaches 750 PSI, the autobrakes are disarmed, allowing the pilot to control deceleration.

What’s that last selection?

Ah, yes RTO.

When arming conditions for RTO are met, (basically equates to T/O config + aircraft accel to greater than 80 kts and then thrust levers reduced to idle) then full Hyd press is supplied to the wheel brakes to stop the aircraft. No decel rate is considered – the maximum stopping force is commanded. Once again though, the anti-skid can interrupt pressure to a brake unit if a lock-up is sensed.



if memory serves, The 744 autobrake selector scale equates directly with the pressure supplied to the brakes. eg. AB1 = 1200psi, AB2 = 1600psi, AB3 = 2000psi to RTO = 3000psi. The rotary switch could just as easily read pressure rather than 1 - 5.
(ref AMM auto brake test)

No, no, no my friend. Do not confuse a “test” with the actual operation of the system. You are correct with a pressure limit, however it is an OR type system. For auto “3” it will be decel of 6ft/sec/sec OR a maximum of 1750PSI.

During a ground test of the autobraking system, it is possible to check the integrity of the system by installing a pressure guage on 1 brake unit of each truck and meeting the autobrake arming conditions. When the brakes are applied by the autobrake system the following pressure should be recorded on the brake gauges for each selected level of braking:-

1 = 1300PSI
2 = 1500PSI
3 = 1750PSI
4 = 2050PSI
MAX = 3000PSI

These pressures are also the MAXIMUM that can be applied at each level of braking during normal ops. Testing and certification data deem that the required decel level can be achieved during all normal conditions within the max pressure limit. But hey, if you want to land your Jumbo on a sheet of ice, don’t think that selecting MAX on your autobrake selector will guarantee that you’ll pull up. You can’t beat the laws of physics!




Bolty, I fear that all your recent time spent playing with the “Sky Skoda”, “The Hyundai of the Sky” , “The Runway Renault” has pickled your brain. Time to turn right when you walk out on the ramp and get re-acquainted with the “Queen of the Skies”


But then again, why believe me? From Mister Boeing:-




AUTOBRAKE SELECTOR MODULE


The Autobrake Selector Module commands a level of
deceleration for landing autobrake operation. The commanded rate of
deceleration and maximum available pressure increase at each switch
position from 1 thru MAX AUTO.

Landing Autobrake
The Autobrake Selector Module Switch will magnetically latch in a
landing autobrake position, when arming requirements are met, to
provide power and a commanded rate of deceleration to the
Autobrake System.
The Autobrake Card will command brake pressure by opening the
Solenoid Valve and will modulate the Control Valve to maintain the
selected deceleration to a complete stop, provided the average
velocity of the 4th, 5th, 6th and 7th fastest of the eight forward
wheels exceeds 60kts and stays above 30 kts for 3 sec, setting a
latch to allow full stop braking.
The wheel spin up latch is reset a air mode signal or system
disarmed or system turned off.

Full hydraulic system pressure is applied during RTO with no rate of deceleration computation.

Autobrake Card
The Brake System Control Unit (BSCU) contains a digital,
microprocessor controlled autobrake card which operates a solenoid
and control valve in the Autobrake Pressure Control Module.

Pressure Control
When the Apply logic is satisfied the Autobrake Card will command
the Control Valve to provide the following;
• Brake Fill
- An initial pressure spike of 1650 psi, for pilot feel.
• Followed by on-ramp pressure
- Pressure increase of 150 psi/sec for 2sec, followed by 450
psi/sec to autobrake selected pressure or deceleration rate
pressure.
• Maintain the selected deceleration to a complete stop

Operation
The module is connected to the Normal Braking System and meters
pressure to the brakes in response to brake system control unit
inputs.
• A solenoid shut off valve controls pressure into the Module.
• A control valve provides a controlled (metered) pressure output.

A pressure switch (750 +/- 50 psi) is installed on the Brake Metering
Valve side of the Shuttle Valve to provide an landing autobrake
disarm input to the Autobrake Card.


Test Application
The AUTOBRAKE APPLICATION test is run to verify proper
operation of the autobrake subsystem for all autobrake settings.
After all preconditions have been met, each arming level on the
switch may be tested separately by depressing START TEST.
• The test energizes the Autobrake Solenoid Valve and increase the
Command Valve pressure up to the set limit.
1=1300psi
2=1500psi
3=1750psi
4=2050psi
MAX=3000psi
• The pressure is maintained for 10 seconds, then reduced to
minimum pressure for 15 seconds.
• When the brakes are released the CMC message will no longer be
displayed and the autobrake switch will disarm.
The test is inhibited with airplane in motion.


Now how did this conversation start? Landing SOPS. What determines these aside from safety.........money!
The longest life of carbon brakes (reduced overhaul cost) can be achieved by using them at a highish temperature and using them for one longish/hard application rather then several short sharp ones. Just watch those F1 drivers jump on the anchors during the warm-up lap. It's mainly used these days to "warm-up" the brakes so as you can have your discs up to optimum operating temp to allow you to go deeper and harder into the first corner and steal a place. I digress........Best way to achieve optimum temps on landing is to let the brakes do a fair share of the work and you can ensure they do this by limiting the use of other deceleration devices (i.e idle/no reverse). Another way is to select a higher level of autobrakes to ensure the brakes are applied to ensure heat build-up to effective temps.

Clear as mud I'm sure. :ok:

Spanner Turner
15th Aug 2007, 16:22
Further to the above:

Obviously as the name suggests, the BSCU can only control the level of wheel braking to meet the target selected - not the maximum overall aircraft deceleration. So if for example autobrake "1" was selected (a target decel of 4 ft/sec/sec) and all manner of decel methods were employed (select reverse, deploy speedbrakes, land on an upslope, land in quicksand, land and have all the passengers put their feet out on the ground or land and deploy a braking parachute) which resulted in a decel rate of say 5ft/sec/sec then there is nothing that the BSCU can do about it. In this case it will command nil Hyd Press to the brake units as it "sees" the required decel rate and is fat, dumb and happy.

Bolty McBolt
16th Aug 2007, 05:05
Spanner
Thanks for taking the time to educate me in the ways of the 744 auto brake system. Now I don’t have to look up my notes as my memory module has been reset. Yes, working the Peugeot fleet does tend to cloud the memory on how proper aircraft work....

londonmet
16th Aug 2007, 23:23
I am not a 747 driver but just as a thought ......

AB level controls rate of deceleration. Use of reverse, be it full, idle or none at all doesn't effect landing distance just the wear and tear on the brakes. So QF's change in SOP's would mean they want you to stop in a shorter distance but in order to save some wear on the old brakes is AB3.

L Met