No Autobrake Arming with Gear Lever Up (747-400)?

[NSEU]

I've read on another forum that Autobrake arming is inhibited with the gear lever UP in one of BA's sims. Is this correct? I can't find any logical reason for it in my old Engineering manuals.

Thanks.

[Dufo]

Interesting. I do not recall this from ground or sim sessions. It is not mentioned anywhere in maintenance manuals.

[wiggy]

Seems a bit strange, though "it's been a while"...of course the gear lever would normally be positioned at "off" after take-off unless you were dealing with one or two of the gear "non-normals", and there are also one or two non-normals where you can't arm the autobrake regardless of gear or gear handle position.

Just a guess but is there any chance there was a bit more to the original story than just the gear lever being at "up"?

[yotty]

Autobrake arming logic
(a) The system arms and latches with a magnetic latching switch when these conditions are met.
1 A deceleration selection (level 1, 2, 3, 4, or MAX AUTO) has been set.
2 No normal antiskid system malfunctions have been detected by the BIT.
NOTE:
If antiskid fault indications for any wheel have been turned off using the switches on the front of the brake control unit, that fault indication will not disarm the autobrake system.
3 No autobrake malfunctions have been detected by the BIT.
4 Correct IRS signals are transmitted to the brake-system-control unit (GND SPEED, PITCH ANGLE, and ACCELERATION only).
5 Brake metered pressure switches on the autobrake shuttle valves show low pressure.
6 Primary and alternate air/ground signals from the Proximity-Sensor-Electronics-Unit (PSEU) are in the air mode or all 4 thrust levers are in idle.
7 Normal brake system is pressurized.

[wiggy]

The antiskid failure (which as you point out could be for a varity of reasons) and subsequent inability to arm autobrake was oft seen in the sim.

As for anything else sadly I don't have access to 744 manuals at the moment - For those not familiar with the machine the gear lever has three positions and normally was placed to "Off" after takeoff once the gear has retracted and the gear doors were closed. The only situation I recall where you would fly around with Gear selected to "Up" was for a Gear Door (or similar) warning after takeoff, where you'd be trying to force and then hold the recalcitrant doors closed by the hydraulic systems, but I don't remember any comments in that NNC about then being unable to arm autobrake prior to selecting Gear down, but as I said it has been a while.....

[NSEU]

Originally Posted by yotty

Autobrake arming logic....

7 Normal brake system is pressurized.

I assume you mean that #4 hydraulics system is available, rather than the brakes being pressurised.

5 Brake metered pressure switches on the autobrake shuttle valves show low pressure.

Despin is active when the gear lever is UP (via the alternate braking system), but the brake metered pressure switches are only on the normal system.

I believe it was routine on KLM to leave the gear lever in UP. I'm not sure if it was a temporary thing or permanent (after a series of maintenance induced incidents causing doors to open in flight).

Hopefully someone could try this in another sim.

Thanks.

P.S. Sorry for the slow response. My PPRuNe notifications don't seem to be working.

P.S. The gear lever only puts out DOWN and NOT DOWN electrical signals. If the BA sim is correct, the Autobrake system must be looking at something other than handle position.

[space-shuttle-driver]

BA SIM Nr. 3 (non RR-engines) does not do what you describe.
I have not flown the other 2 SIMs.

[eckhard]

I'm in #4 tomorrow night and will take a look.

[Long Haul]

For many years the KLM policy was to keep the gear lever in UP from after takeoff until extension before landing, although this changed recently due to a movement towards basic Boeing procedures. I never had any problem arming the autobrakes with the gear handle in UP.

[NSEU]

Thanks, gentlemen.. All answers much appreciated.

[Jetjock330]

The autobrake doesn't like to arm in a simulator if the park brake is still set from re-positioning. Try release the park brake if set, and then set the auto brake.

[NSEU]

Thanks, Jetjock. On the ground, I know Autobrake logic won't allow the switch to be set if the brakes are parked (as there is pressure in the "metered" brake lines). In the air, with the landing gear lever in OFF, is all hydraulics removed from the landing gear, or just from the retraction/extension system? I originally believed all gear systems, but looking at the brake hydraulic schematics, unless I've overlooked something, I don't see how this can be true.

[eckhard]

BA Sim #4 auto brake arms ok with the gear lever in UP.

[NSEU]

Thanks! The original question was raised because (I'm told) the unusual behaviour occurred on Sim #4. It seems the problem has gone away or there were other factors at play (suggested by another poster).