E jet autobrake

[charlie226]

How can you check that the autobrake is giving you the requested decceleration rate ? What happens if you don't get the requested decceleration ? Will the autobrake switch itself off or do we get an Eicas message ?

[ab33t]

I think you need to monitor the braking , if you just sit back and relax you may find out to late that there is no more runway to stop on.

[FE Hoppy]

Firstly do you know what the requested decel rates are?

RTO - max pressure. No specified rate.

Landing
low,Med,Hi

No published decel rate.

For anyone who likes their trivia the rates are 4,8 and 13 ft/s^2 but the only place you will find those numbers are in the manufacturers system description reports. They don't appear in any of the operational documents as you don't have a decel meter with which to measure normally.

I say normally because if you have HGS with HUD3A certification then you get low Med Hi markers on the combiner display and the accel pointer will then show if you are achieving the selected rate.

The Autobrake uses the current decel rate compared with the requested rate to calculate the brake command in the landing mode. The aircraft not achieving the requested rate will simply cause the AB to request more pressure.

The AB will declare "FAIL" if it looses communication or has an internal fault. This will cause the selector to go to the OFF position and the EICAS " AUTOBRAKE FAIL" message.

[Chesty Morgan]

Hoppy, aint that HUD thingy brill.

Can you confirm though that RTO is max pressure and not a set rate? I've recently had a heated discussion with a line trainer who claims it's a set decel rate and that if you use reverse the brake pressure will release slightly.

I'm in your camp though and can't see why it would only be a set rate.

[FE Hoppy]

Hi Chesty,

The problem may come from the the aom description note:

NOTE: RTO is the selected takeoff mode with the maximum
deceleration rate. This deceleration is equivalent to the
maximum manual braking.

This is a slight miss quote from the certification document which says:

RTO Maximum available deceleration

and

RTO select is equivalent to full brake pressure application

It's not the deceleration that is equivalent. It's the signal requesting pressure from the BCMs. This signal is equal to full brake pedal compression i.e max brake pressure.

There is a lot of this in the AOM. In this case we have German engineers writing the original reports and then those reports being interpreted by Brazilian engineers all working in English so you can't blame them...............



So stick to your guns.

[charlie226]

Thank you very much FE Hoppy for the comprehensive answer. In my airline we monitor the decceleration with speed callouts by the PNF. Up to now I've had good expereince with this autobrake and this system is IMHO another example of a nice balance between sophisticated automation and human monitoring and action by Embraer.