United B777 #830 SYD Center Hydraulic System Failure

loss of the center system hydraulic

system in the Boeing trip 7 is a big

deal because most of the components

hydraulically operated components on the

Boeing trip 7 are located on the center

system but thanks to the excellent

design of the aircraft and the

redundancy built into this aircraft

there's no problem continuing to operate

the aircraft however this represents one

of the most labor

intensive emergencies that a flight crew

can face in the trip 7

and United had to deal with this

recently on a departure out of Sydney

let's check it

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out

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it's been very tough tough keeping up

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lost a quick update to the Lost wheel

story on the United Tri 7 out of San

Francisco that diverted to Los Angeles

it looks like it was a wheel failure

based on these photographs sent in by a

Blanco Lio viewer the brake assembly is

still shown here on the axle and the

retaining nut and the bolts that retain

the axle retaining nut are in place on

the axle and this appears to be the

outer race to the wheel bearing on the

outside of the

wheel here's a closer look at the axle

with the retaining nut in place and the

bolts that retain the axle nut in place

there's the

timkin roller bearing and the outer race

located right there so it looks like the

wheel fail just outside of the outer

race and it rolled right off up and over

the retaining nut and off of the

aircraft this aircraft has since been

fixed and returned to service and fed

right back up to San

Francisco regarding the lantom 787 that

injured 50 people who apparently were

not wearing their seat belts when they

should have been in Cruise flight

remember anytime you're in your seat

keep that seat belt fastened the only

information we have right now on that is

some testimony from some of the

passengers and this particular passenger

said that the pilot came back and he

asked the pilot what happened and this

passenger says that the pilot said that

all of his screens went blank briefly

and then

reappeared so until we get the flight

data recorder will we know the story of

exactly what happened to the lantom 787

on its flight from Auckland to Sydney

intermittent loss of power to the

aircraft which essentially to me sounds

like the two main AC the left and right

main AC circuits if there was an

intermittent loss of that power did the

autopilot kickoff suddenly and if the

autopilot kicked off suddenly did the

flight crew overreact and bump the

aircraft in a nose down condition or was

the aircraft out of trim and the

aircraft resumed its trimmed position

with the autopilot off one other form of

turbulence that you can encounter that

can replicate this is if you fly

perpendicular through the Wake

turbulence of another aircraft that has

just passed you'll be in perfectly

smooth air and then you'll hit a huge

bump depending on how close you were

behind the other aircraft as you cross

perpendicular to his wake turbulence

Wham like a big speed bump and then

you're back in smooth air but this

sounds more powerful than just simply

Crossing somebody's wake turbulence and

there was no other word of turbulence in

the area prior to this incident so until

we get the FDR then we'll get the rest

of the

story the normal way of raising and

lowering the landing gear on the Boeing

trip 7 is via the center hydraulic

system each landing gear bogey has six

wheels on it to help distribute the

massive weight of the boing Tri 7 which

happens to have a Max gross weight of

777 th000 lb and if we swing around to

the back side of the landing

gear we see four lines four hydraulic

lines two brake lines one there and one

there and then two hydraulic lines that

go to this hydraulic actuator right here

because of the six wheels in order to

turn the Boeing trip 7 while T ing on

the ground especially at tight 90° turns

below 10 knots the rear two wheels of

the bogey pivot like a large truck in

order to prevent scrubbing of the tires

and allow you these tighter turns and

this is facilitated using this pivoting

arm located right here and this

hydraulic actuator located right here

powered by the center hydraulic system

and connected in association with the no

no wheel steering system and the tiller

up in the

cockpit so as captured by PL spotter New

York Aviation United's flight 8:30 on

Monday the 11th of March departing

Sydney he captured this failure of the

hydraulic system there you can just see

the hydraulic fluid missing out of the

right side landing gear right upon

initial

departure there's that fluid leaking out

right about in that same area we were

just talking about in the landing gear

so it's more than likely one of those

flexible lines and it's pretty common if

you're going to lose a hydraulic system

especially a center hydraulic system it

usually occurs when one of these

flexible lines fails that is attached to

the landing gear and this flexxable line

has to undergo a lot of flexing and

motion as the gear is retracted and

extended and these hydraulic lines do

have a life limit on them and they're

they're dated and banded and so you know

when to replace them according to date

but sometimes they fail before they

their time is expired to replace them so

that's a relatively small hydraulic line

in a large hydraulic system maybe some

of you maintainers can tell us exactly

the center system Reservoir quantity

here but it's going to take a while for

this system to leak down to the point

before the pilots even get a warning of

either Center system quantity low or

Center system pressure low it could be

that perhaps somebody on the ground

notified the crew of the aircraft that

they noticed something leaking out of

the right main landing gear of the

aircraft on departure a quick review of

the redundancy of the Boeing Tri 7

hydraulic system you've got three

separate hydraulic

systems any one of these can power all

of the primary flight controls of the

aircraft any one single system as each

of the primary flight controls are

connected to each of the hydraulic

systems each hydraulic system has

several sources of power the left

hydraulic system has the left engine

driven hydraulic pump and an electric

demand pump the right hydraulic system

has the same thing the right engine

driven hydraulic pump and the right

demand pump the center system has two

large pneumatic pumps using bleed air

from the system to power and they are

demand pumps so they come on when

they're needed and it also has two

electric pumps as well to back that up

so a series of four pumps to power the

center system hydraulic system any one

of which can power the the entire system

but when these gear when the gear and

flaps are in motion it does require a

large volume of hydraulic fluid and

there's also the backup of the ram a

turbine the rat which can provide some

Center hydraulic system trapped fluid to

the primary flight controls in the event

of a either a loss of both engines or B

a loss of both main AC electrical

systems or or see a loss of all three

hydraulic systems again this fluid is

trapped in the center hydraulic system

so that in the event of a leak like this

from the landing gear this fluid will be

trapped separate from that system so

here on flight rate r24 looks like the

crew took off about 130 a.m. Zulu and

headed out about 40 minutes or so before

turning back and coming in land again

this is a labor intensive emergency but

it's not a Time constrained emergency so

you've got all the Time in the World to

sort this out especially when you have

enough fuel to fly all the way from

Sydney to San Francisco and you've got a

bunch of checklists to cover once you

get into the loss of Center system

pressure or quantity checklist it's

going to direct you into how are you now

going to lower the landing gear and the

flaps you're going to have to use the

alternate landing gear extension and

checklist and the alternate flap

extension and checklist the alternate

gear extension on the Boeing Tri 7 uses

a DC operated motor I assume off of the

battery or hot battery bus to unlock the

up loocks to the doors and the landing

gear and allow the landing gear to

freefall the flaps have an electrical

alternate extension system which

bypasses the hydraulic system altogether

but is a very slow system to lower the

flaps so you got to allow for a lot of

time to very slow slowly lower the flaps

also you're going to be getting into

your emergency landing checklist you got

to have go around considerations now

that your gear and flaps are kind of

stuck in that position what are you

going to do in the event of a go round

well you're going to be using a flaps 20

Landing you're going to be landing with

considerably less flaps than you

normally would flaps 20 the same thing

you would do for a single engine Landing

again for go round

considerations in a normal Greaser

Landing in the Boeing trip 7 and this is

why I love this airplane so much the

gear is tilted up like this so you can

just roll those bottom two wheels onto

the runway and then the gear will slowly

tilt forward and then each of the six

wheels will contact the the runway

individually not all at once and so it

just makes for buttery smooth Landings

and an excellent suspension in the oo

struts of the Boeing Triple

7 getting that ground effect

and just roll it on like that just like

butter note also the automatic spoilers

deploying as soon as the weight on the

wheel switch senses weight on the wheels

the auto spoilers

deploy now in this picture from New York

Aviation of the emergency return of

United

Airlines the experienced Triple 7 guy

will know right away that's Center

system hydraulic system failure note the

doors are still down in the open

position normally the doors close behind

the landing gear once it's

extended indicating that they had use

alternate gear extension gravity to get

the gear down and also the landing gear

is not tilted for landing the Tilt

system does not work on emergency gear

extension it just gravity drops the gear

down into the position that it was when

it was

retracted and as we watch this unfold

flaps 20 Landing

boom all six wheels on each bogey hit at

once causing a bit of a Lurch and then

the spoilers need to be manually

deployed so the pilot manually deploys

the spoilers after

landing instead of them automatically

popping out right as soon as the weight

on the wheels is sensed boom normally

they would pop out right there he gets

the nose wheel he's got the aircraft

under control okay let's deploy the

spoilers and come out to a roll out to a

complete and uneventful stop the thrust

reverses of course still work because

they're work operating off the

individual hydraulic systems left and

right and the main landing gear doors

have plenty of clearance to clear the

runway in the open condition during this

Landing wheel brakes Auto brakes and

Anis skid are still operating normally

as they are all operated off of the

right hydraulic system

right here regarding the redundancy of

the braking system on the Boeing trip 7

normal brakes are on the right system

alternate brakes and Reserve brakes are

on the center system and then there is a

accumulator for a fourth way to get this

aircraft stopped plus you have these two

isolation valves to help trap that fluid

for alternate and Reserve brakes over 2

hours later after the aircraft landed

looks like there was still some

hydraulic fluid leaking out of this line

and hitting the hot brakes over here but

the ARF took care of that no problem and

all the passengers deplan the aircraft

back at the gate uneventfully so good

job of the flight crew of United's

flight 8:30 out of Sydney back on Monday

doing one of the most labor intensive

emergency procedures that you can handle

in one of these aircraft but this is

exactly what we train for constantly in

the simulators the checklists are there

the training is there good job thank you

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