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Park Brake Set - Upper EICAS Annunciation

Started by Roddez, Sat, 21 Sep 2019 20:42

Roddez

A couple of days ago I was crawling around under the cockpit floor, looking for the Park Brake Set micro switch.  Eventually I found the little sucker, but it's behaviour was a little different to what I have come to expect from PSX.

When the brakes are off and the parking brake handle is down, the normally open contacts of the switch are indeed open.  The picture below shows the micro switch and you can see that the roller is not in contact with the cam that is attached to the parking brake lever.



When lifting the handle up, but NOT depressing the toe brakes, you will see that the cam rotates and the switch roller is in contact with the cam.  However this does not trigger the micro switch which means there will be no upper EICAS Park Brake Set message.



When you depress the toe brakes and lift the Park Brake handle, the cam rotates further and the micro switch does engage.



So, my question is simple:
1.  Is this switch out of alignment?
2.  Is the switch correctly aligned and the Park Brake Set annunciation will not trigger simply by just raising the handle.
3.  It's an airline option and anything goes... ;)

I have not had a chance to look at the AMM to see what it says, but then again if it's airline specific then two different manuals will likely contain two different answers. ;)

Cheers,

Rod.
Rodney Redwin
YSSY
www.simulatorsolutions.com.au

John H Watson

QuoteWhen you depress the toe brakes and lift the Park Brake handle, the cam rotates further and the micro switch does engage.

Interesting. This mechanism was studied during beta testing. I don't know if it was an adjustment issue, but I recall trying it on a couple of real world 744s and the message appeared (without the pedals depressed). I think someone on the forum found the opposite to be the case post-PSX release (not sure if it was in a big sim or on the real aircraft).

The switch adjustment is done with the brake pedals fully depressed, but with a (temporary) 1/4 inch shim between the pawl and the bellcrank. I don't know if the shim compensates for wear and tear over the years. Rig pins are involved in the adjustment.

Anyway, depending on what version of the AMM you have, there are lots of pictures on how to do the adjustment. Hopefully this agrees with PSX. I very much doubt that there are airline options for this.


Hardy Heinlin

I just learned that an engineer at Virgin Atlantic just confirmed that the message will not appear just by pulling the lever while the pedals are released.

Maybe the reference that was used for PSX is or was a company modification indeed?


|-|

Gary Oliver

Hardy,

Although not at all the same as the real aircraft we have run into several people thinking they had set the parking brake in our sim, seeing the EICAS message and the plane rolling forward.

Our Parking brake handle is effectively a microswitch with a solonoid on it to pull it down.

What happens is someone doesn't depress the pedals fully, they lift up the handle which sets ParkingBrakeHandle to 1 in PSX, and then they release the pedals which unlike the real aircraft to not latch down and the plane starts rolling.

The added benefit of changing PSX to not display the message unless the brakes are really set in PSX should stop this happening.

Cheers
G

the mad hatter

I had the same issue with the park brake and setting it, i.e  it would be set (via the aircraft micro switch) and the aircraft would roll fwd, we took a different approach for conflict resolution and wired to the arinic cards as these are more stable.. now everything is tickety boo  mostly  ... at times when the sim is first started and at the gate with park brake set the the aircraft will roll forward with no way of stopping it other than a complete reset.

John H Watson

QuoteWhat happens is someone doesn't depress the pedals fully, they lift up the handle which sets ParkingBrakeHandle to 1 in PSX, and then they release the pedals which unlike the real aircraft to not latch down and the plane starts rolling.

The real aircraft would roll if you didn't depress the pedals fully. If you don't depress the pedals fully, the pawl (on which the microswitch arm roller runs) won't mechanically latch on the pedal mechanism and the pedals would spring back up. When this happens, hydraulic pressure from System 4 or from the emergency accumulators can't get to the brakes.

Pulling on the park brake handle activates the park brake microswitch. The park brake microswitch closes the park brake valve which is a device to stop hydraulic pressure (applied by having the pedals depressed) from bleeding out through the antiskid valves. The different test results are most likely due to wear and tear, not because of some pointless airline modification.

Roddez

Hi Hardy,

According to one AMM:
Quote
When the parking brake lever is pulled, the movement of the linkage sets a micro switch. This passes power from the PARK BRAKE circuit breaker on the P6 panel to the close fields of the electric motor on the parking brake module. When the electric motor has cycled to the closed position, power and ground are provided to turn on the Parking-Brake-Valve-Closed Relay.

When the relay switches it establishes a path from the electrical interface units (EIUs) to ground, and
this permits the PARKING BRAKE SET indication to appear on EICAS.

Further in the manual, there is information about testing the operation of the parking brake.  Whilst this next section doesn't specifically reference the upper EICAS message, I read this to suggest that the parking brake message won't display because the parking brake is not engaged.

Quote(a) Push on the captain's left brake pedal and pull the parking brake lever on the control stand.
1) Make sure the parking brake will not engage.
(b) Push on the captain's right brake pedal and pull the parking brake lever on the control
stand.
1) Make sure the parking brake will not engage.
(c) Push on the first officer's left pedal and pull the parking brake lever.
1) Make sure the parking brake will not engage.
(d) Push on the first officer's right pedal, and pull the parking brake lever.
1) Make sure the parking brake will not engage.

To provide a definitive answer, I will try and follow the instructions in the AMM and use rigging pins and shims to calibrate the parking brake micro switch in a cockpit here in Sydney.  This might make a good exercise for some of us during WorldFlight.
Rodney Redwin
YSSY
www.simulatorsolutions.com.au

Avi

We can ask Gilad to make a test (and if he isn't a pilot - and I think he is, he knows one)  :)
Avi Adin
LLBG

Hardy Heinlin

Gilad is 100% a 744 pilot :-)

We've got confirmation now from various airlines that the pedals need to be depressed for the message. I'll modify PSX accordingly and I won't make it a company option.


|-|ardy

the mad hatter

#9
Hang about we must be doing something either right or wrong, we use the aircraft components including P6 circuit brker, which functions, this in turn is wired to the aircarft nose gear landing light ( real ) when the parkbrake is on (depressed) pedals down parkbrake lever up, we get the red light on the nose gear box and the message in the flightdeck stating it is on when the parkbrake is released both the light and the message disappear (the rolling is related to a card issue) not PSX

I kinda think because I have a Frankin sim that because there is no Hydraulics the actual aircraft components is not seeing them ? and therefore PSX does not see them when the sim is first started and a reset is required, when the sim is restarted I am guessing the hydraulics system is pressurized in PSX and the aircraft see them thus the rolling stops.. but this is just a wild **** guess 

Hardy Heinlin

Modification of "PARK BRAKE SET" message logic is now available in PSX version 10.91:

http://aerowinx.com/board/index.php?topic=4191.0


|-|ardy

John H Watson

Quote91.01. EICAS memo message "PARK BRAKE SET" now requires both pedals to be depressed (source: Virgin Atlantic).

In theory, it would be possible to park the brakes using the left pedal on the captain's side and the right pedal on the F/O's side (and vice-versa) because of the mechanical linkages. Is the message similarly programmed?

Roddez

Quote from: John H Watson on Fri, 18 Oct 2019 01:35
In theory, it would be possible to park the brakes using the left pedal on the captain's side and the right pedal on the F/O's side (and vice-versa) because of the mechanical linkages. Is the message similarly programmed?

John,

Qs357="Brakes" only supports two values; Left & Right.  Further, given the toe brake pedals are mechanically linked, I suspect the answer would be yes.

Rod.
Rodney Redwin
YSSY
www.simulatorsolutions.com.au

Hardy Heinlin

Yes, there are just two variables -- left and right -- as both pedal pairs are mechanically linked, and they will never break in PSX.


|-|-|-|ardy

John H Watson

Thanks. I was just wondering what would happen if a home cockpit had two independent pedal sets. I guess it would depend on how it was hardwired into PSX.

United744

Moot now, but I thought the parking brake sensor had to see hydraulic pressure at the brakes in addition to the brake handle being pulled, in order to apply the parking brake, hence the requirement for the brakes to be depressed to set them.

John H Watson

QuoteMoot now, but I thought the parking brake sensor had to see hydraulic pressure at the brakes in addition to the brake handle being pulled, in order to apply the parking brake, hence the requirement for the brakes to be depressed to set them.

Hydraulics has nothing to do with it. The logic looks at park brake lever position (detected by the switch shown in the photos above) and park brake valve position (detected by switches on the valve).. The park brake valve does not require hydraulics to open and close. It's just an electric motor-driven valve controlled by the park brake lever mechanism switch.

Latching the park brake pedals down requires the brake pedals to be pushed about 98% of full travel, otherwise a mechanical pawl attached to the park brake lever mechanism won't engage on the rudder pedal mechanism.... The pawl hits the wrong part of the latching mechanism and the pedals can't be latched in position. However, I have seen the message on at least one aircraft without hydraulics and without pushing the pedals, so improper mechanical adjustment and/or wear and tear, it seems, can generate the message.