Typical pilot question....787 tow in at end of flight- should Hydraulics be on or off

[RMC]

Our procedure for a final tow onto stand used to be .....Park brake on, eng shut down, HYds and beacon off, once ground crew in contact and report ready to tow beacon on and parking brake off.
Recently (I believe for 777 commonality re hyd braking) we changed to leaving hydraulics and beacon on.
The main question I have is if the steering is not locked out by the ground crew ( there is no cockpit procedural requirement to check this) and the hydraulics were on could the HYds being on damage the nose gear steering.
I do not have a nose gear steering servo description / schematic but assume that if a turn was made with the original procedure (hydraulics off) then any pressure (assuming there was an NRV retaining it) would immediately dissipate to return through the servo. Thanks in advance.

[Exup]

Don’t know about the 787 but every other aircraft I’ve worked towing is carried out with Hyd on & steering bypass pin installed. Procedure is no different from when you push back off stand on departure.

[Wodrick]

Doubt that the steering would be damaged as the tow bar would shear (shear pin) PDQ.
Don't think it would matter with the type of tractor that secures the whole assembly and lifts it clear of the ground.

Just an opinion.

[RMC]

With it’s electric braking the 787 doesn’t need hydraulics for brake operation ( unlike the 787 which has cross pilot rating). I can’t see any other reason apart from standardisation of types why the 787 would need hydraulics during a tow.

[Cough]

RMC - I believe you are correct with the 777 rated pilots keeping procedures standardised. Out procedures also have in the before start cx's, R hyd demand pump on before the others which is another carryover.

[eckhard]

Here’s the relevant section from our 787 FCOM. Apologies for formatting. My bold.

The main point is that the four hydraulic pumps remain in AUTO until the towing procedure is completed.

Shutdown Procedure
Start the Shutdown Procedure when approaching the parking stand.

APU selector (as needed) START, then ON
P2
External Lights As Required
P2
Instruct the Cabin Crew to disarm the doors.
P2
PA: call “CABIN CREW DOORS TO MANUAL AND CROSSCHECK”
Parking brake Set
P1
Verify that the PARKING BRAKE SET message is shown.
Electrical power Set
P2
If APU power is needed:
Check that the APU RUNNING message is shown.
If external power is needed:
Verify that the FORWARD EXTERNAL POWER L AVAIL light is illuminated.
FORWARD EXTERNAL POWER L switch – Push
Verify that the ON light is illuminated.
If the FORWARD EXTERNAL POWER R AVAIL light is illuminated:
FORWARD EXTERNAL POWER R switch – Push
Verify that the ON light is illuminated.
Call “SHUTDOWN”
P1
FUEL CONTROL switches CUTOFF
P2
If towing is needed:
Ground handling personnel Establish communications
P1
WARNING:
If the nose gear steering is not locked out, any change to hydraulic power with the tow bar connected may cause unwanted tow bar movement.
Nose gear steering Verify locked out
P1
CAUTION:
Do not turn the nose wheel tiller during pushback or towing. This can damage the nose gear or the tow bar.
CAUTION:
Do not use airplane brakes to stop the airplane during pushback or towing. This can damage the nose gear or the tow bar.
Parking brake Set or release
P1
Set or release as directed by ground handling personnel.
SEAT BELTS selector OFF
P2
CAUTION:
Verify Passenger DOORS MANUAL EICAS before selecting SEATBELT selector OFF.
HYDRAULIC panel Set
P2
LEFT ELECTRIC DEMAND pump selector – OFF
CENTER 1 and CENTER 2 ELECTRIC pump selectors – OFF
RIGHT ELECTRIC DEMAND pump selector – OFF
FD DOOR POWER OFF
P2
FORWARD CARGO AIR CONDITIONING control OFF
P2
Note:
Set the control to OFF to minimise the risk of FCAC failure during ground operations.
FUEL PUMP switches OFF
P2
BEACON light switch OFF
P2
FLIGHT DIRECTOR switches OFF
P2
TRANSPONDER MODE selector 2000, STANDBY
P2
Local airport regulations may require an alternate code to be selected.
EFB CLOSE FLIGHT Select
P1, P2
HUD combiner Stow
P1, P2
Note: To prevent the possibility of injury, ensure the combiner is fully raised and securely latched in the stowed position.
Status messages Check
P2
Note: Disregard EICAS alert and status messages displayed during the PFC self test after hydraulic shutdown. Wait approximately 3 minutes after HYD PRESS SYS L+C+R message is shown before recording status and alert messages in the maintenance log.
APU selector As needed
P2
Call “SHUTDOWN CHECKLIST.”
P1
Do the SHUTDOWN checklist.

[Cough]

Eckhard,

I don't think RMC or I disagree with what's written. But as RMC notes, because the brakes are electric on the 787, is there actually a need to run the hydraulics during the tow? More a theoretical question than a procedural one.

Personally I think not, except for the common type rated flight crew where hyd power is needed for the brakes on the triple...

[eckhard]

Yes, I see what you mean. The ‘Towing Power Mode’ of the electrical system (used when towing to/from the hangar) does not energise any hydraulic services, so I agree that the ‘towing in procedure’ described above leaves the hydraulics on simply to provide commonality with the 777.