B777 - Loss of L HYD

[Jr. Airman]

Hello,

Just wondering if anyone could verify if whether a Loss of the L HYD system will lead to loss of AUTOLAND capability on the 777. If so why?

Couldn't find any literature relating to it, although had this problem occur to me in the Simulator. Wondering if it was a SIM fault...

cheers!

[Cubbie]

It is not a sim fault, loss of the left Hydraulic results in loss of autoland, its mentioned in the 777cbt.

[Jr. Airman]

Thanks for that. Went back and did the same, only CBT makes reference to L HYD failure leading to NO AUTOLAND. Nothing in any of the FCOMs or QRH.

Also does mention that both L & R systems are similar so just curious as to why only loss of L system leads to NO AUTOLAND and not the R system too.

The manuals say that both L & R systems power various Flight Controls & Onside Thrust Reversers and the R system additionally powers Normal brakes.

Still would be glad to hear if anyone's got more info on this....

cheers

[MBA747]

For Autoland, elevator needs a minimum of 3 actuators. If L. Hydraulic system is lost 2 actuators are lost. Hence no Autoland.

[Jr. Airman]

MBA747 - Many thanks for that sir!

[wolkenjaeger]

It may be a little bit picky, but would you mind state the source to this?

[FCeng84]

B777 has three hydraulic systems and four elevator actuators (two actuators on each elevator surface). The L and R systems each power one elevator actuator (L hyd powers L elevator, R hyd powers R elevator). The C hyd system powers two elevator actuators, one on each of the two elevator surfaces.

[my salami]

The Aircraft is perfectly capable to perform an Autoland with the L HYD System failed.
It's just a liability/certification issue.

From the B777 AFM

Demonstrated compliance with the AFDS airworthiness performance and integrity standards does not constitute approval to conduct operations in low weather minima conditions.

Automatic Landing With One Engine Inoperative The autopilot system has been demonstrated to perform satisfactory automatic landings with one engine inoperative at the beginning of the approach. The demonstrated configuration was:

LAND 3 OR LAND 2 annunciated Flaps 20 or Flaps 30

The automatic landing system has been demonstrated to perform satisfactorily with one engine inoperative in the following wind conditions:

Headwind: 33 knots Tailwind: 20 knots Crosswind: 29 knots

The performance was demonstrated with and without autothrottle on the operative engine, and with and without Thrust Asymmetry Compensation.

The automatic landing system has been demonstrated to perform satisfactorily following an engine failure during approach.


Automatic Landing With A Single Hydraulic Failure The automatic landing system has been demonstrated to perform satisfactorily with a single hydraulic failure to either the left, center or right system.

Verification Altitude For Autoland

On approach for autoland, verify LAND 2 or LAND 3 status, as appropriate, at 500 feet AGL.

Normal Procedures 777 Airplane Flight Manual .

Section Autopilot Flight Director System, continued from previous page A121788

[JammedStab]

Thanks for that. Went back and did the same, only CBT makes reference to L HYD failure leading to NO AUTOLAND. Nothing in any of the FCOMs or QRH.

Also does mention that both L & R systems are similar so just curious as to why only loss of L system leads to NO AUTOLAND and not the R system too.

The manuals say that both L & R systems power various Flight Controls & Onside Thrust Reversers and the R system additionally powers Normal brakes.

Still would be glad to hear if anyone's got more info on this....

cheers

I discovered that on my initial sim training as well. The IP was not aware of this. It should be mentioned in the QRH in my opinion. Otherwise, you may not discover this until near landing at destination with much less options available depending on the weather.

[FCeng84]

ibmpilot - I stand corrected, thanks for pointing out my error. I think I was confusing the 787 and 777. The 777 Left Hydraulic System does power two of the four elevator actuators. This distribution was chosen in conjunction with the hydraulic power for the two horizontal stabilizer control motors (one on C Hyd, the other on R Hyd). With is arrangement, loss of two hydraulic systems leaves you with either one elevator surface and the stabilizer active or no stabilizer, but both elevator surfaces powered.

Losing the L Hydraulic system will drop the system from the nominal two actuators on each elevator surface to only one active on each surface. In that situation horizontal stabilizer control is not compromised as it is not controlled by L Hyd.

[agg_karan]

Request the source for information regarding - " for autoland, elevators need 3 actuators"
Tried to search in AMM couldn't find.
Greatly appreciate your help
:)

[extricate]

Can anyone point us to the right direction?

[agg_karan]

Any book close to - PART 25/ETC AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES ???

[Capt. Flamingo]

The L HYD system powers both elevators (left elevator powered by L+C and right elevator powered by R+L), so loosing the L HYD degrades the elevator authority required for autoland certification parameters I guess.

https://www.google.ae/search?q=b777+hydraulic+power+distribution&oq=b777+hydraulic+power+distribution&aqs=chrome..69i57.16660j0j4&client=ms-android-alcatel&sourceid=chrome-mobile&ie=UTF-8#imgrc=BmKkJ86SXVIwhM: