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Anonz263x
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Can 747s really use flaps even with total hydraulic loss and if so why isnt this on other aircraft?

Tue Nov 23, 2021 6:09 am

Listening to the cockpit voice recorder of JAL 123, has made me surprised to find that apparently the flaps on a 747 can be extended even with total hydraulic loss, but my question is this true for every 747s and why isnt this on other aircrafts for example a DC-10 or would have UAL 232 suffered with the reduction in directional control had the ability to lower flaps was there like JAL 123 did when the flaps were apparently reduced their directional control or in theory what wouldve been the other consequences of it?
 
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ADent
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Re: Can 747s really use flaps even with total hydraulic loss and if so why isnt this on other aircraft?

Tue Nov 23, 2021 8:32 am

Looks like the 747 LE devices are pneumatic or electrically actuated (based on what I see here: viewtopic.php?t=752455 ). A lot of planes use electric screws on the trailing edge flaps.

From AA191 it seems hydraulics are needed for the DC-10 LE devices.
 
jetskipper
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Re: Can 747s really use flaps even with total hydraulic loss and if so why isnt this on other aircraft?

Tue Nov 23, 2021 9:51 am

The 737 has a similar system with a total loss of both systems the LE and TE devices can be extended with an Alternate electric system. Once extended only the TE devices can be retracted. The devices extend at a much slower rate and a Flaps 15 landing is planned.
 
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Kindanew
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Re: Can 747s really use flaps even with total hydraulic loss and if so why isnt this on other aircraft?

Tue Nov 23, 2021 9:59 am

The A380 and A350 are also flyable with a total hydraulics loss as well I believe.
 
Anonz263x
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Re: Can 747s really use flaps even with total hydraulic loss and if so why isnt this on other aircraft?

Tue Nov 23, 2021 10:12 am

ADent wrote:
Looks like the 747 LE devices are pneumatic or electrically actuated (based on what I see here: viewtopic.php?t=752455 ). A lot of planes use electric screws on the trailing edge flaps.

From AA191 it seems hydraulics are needed for the DC-10 LE devices.


I wonder why didnt the DC-10 have this alternate system and would it have caused UAL 232 to lose directional control or worse?
 
VMCA787
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Re: Can 747s really use flaps even with total hydraulic loss and if so why isnt this on other aircraft?

Tue Nov 23, 2021 10:39 am

Sorry, but I am about to rain on your parade! What difference does it make if the Flaps have both hydraulic and electric extension/retraction? You have a much bigger problem staring you in the face! How are you going to control the aircraft? With no hydraulics, you have no flight controls!
 
Anonz263x
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Posts: 38
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Re: Can 747s really use flaps even with total hydraulic loss and if so why isnt this on other aircraft?

Tue Nov 23, 2021 10:59 am

VMCA787 wrote:
Sorry, but I am about to rain on your parade! What difference does it make if the Flaps have both hydraulic and electric extension/retraction? You have a much bigger problem staring you in the face! How are you going to control the aircraft? With no hydraulics, you have no flight controls!


Yes Im aware no hydraulics means no normal flight controls except the engines but Im just surprised that the transcript of JAL 123 that they managed to lower flaps on their 747 before crashing
 
Fixinthe757
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Re: Can 747s really use flaps even with total hydraulic loss and if so why isnt this on other aircraft?

Tue Nov 23, 2021 11:10 am

Yes, the 747 has an electric motor that can move flaps (to answer your question). And yes other Boeings have it as well
 
bigb
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Re: Can 747s really use flaps even with total hydraulic loss and if so why isnt this on other aircraft?

Tue Nov 23, 2021 12:50 pm

The 747 leading edge flaps are pneumatically driven in primary and electrically driven in secondary and Alternate modes. The trailing edge flaps are Hydraulically driven in primary and electrically driven in secondary and Alternate modes.

When operated in secondary and alternate, it takes a really long time for the flaps to deploy….
 
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tb727
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Re: Can 747s really use flaps even with total hydraulic loss and if so why isnt this on other aircraft?

Tue Nov 23, 2021 1:28 pm

The 727 had alternate flaps as well. The trailing edge flaps were off a standby electric pump and they took forever to move. The LE would come down as well but in random order and were locked down when finished, they couldn't be retracted in the alternate mode but the trailing edge could. Again it would take forever to retract so you didn't plan on landing with more than 15 degrees of flaps if memory serves me correctly. You did want to go to at least flaps 5 on extension to unlock the outboard ailerons for more roll authority in case of leading edge flaps coming out unevenly.
 
AA737-823
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Re: Can 747s really use flaps even with total hydraulic loss and if so why isnt this on other aircraft?

Tue Nov 23, 2021 2:47 pm

VMCA787 wrote:
Sorry, but I am about to rain on your parade! What difference does it make if the Flaps have both hydraulic and electric extension/retraction? You have a much bigger problem staring you in the face! How are you going to control the aircraft? With no hydraulics, you have no flight controls!


FALSE.
A 737 will fly all day long with failed hydraulics.
Granted, you’ll want to use STBY RUDDER pumps.
But you speak as though the loss of hydraulics will crash a plane. And in many cases, it won’t. Redundancy on most airplanes, and manual reversion on planes like the 737.

Regarding United 232, I fail to see what difference flap position would have made on that outcome.
 
VMCA787
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Re: Can 747s really use flaps even with total hydraulic loss and if so why isnt this on other aircraft?

Tue Nov 23, 2021 3:16 pm

AA737-823 wrote:
VMCA787 wrote:
Sorry, but I am about to rain on your parade! What difference does it make if the Flaps have both hydraulic and electric extension/retraction? You have a much bigger problem staring you in the face! How are you going to control the aircraft? With no hydraulics, you have no flight controls!


FALSE.
A 737 will fly all day long with failed hydraulics.
Granted, you’ll want to use STBY RUDDER pumps.
But you speak as though the loss of hydraulics will crash a plane. And in many cases, it won’t. Redundancy on most airplanes, and manual reversion on planes like the 737.

Regarding United 232, I fail to see what difference flap position would have made on that outcome.


REALLY? Care to explain how what I am posting is false? The 737 has manual reversion, just like the 727. If you lose hydraulics you still have cables. On ALL models of the 747, if you lose hydraulics, you also lose flight controls. So, all hydraulic failure, you are merely a passenger. If you know differently, I'd love to know.
 
bigb
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Re: Can 747s really use flaps even with total hydraulic loss and if so why isnt this on other aircraft?

Tue Nov 23, 2021 4:23 pm

VMCA787 wrote:
AA737-823 wrote:
VMCA787 wrote:
Sorry, but I am about to rain on your parade! What difference does it make if the Flaps have both hydraulic and electric extension/retraction? You have a much bigger problem staring you in the face! How are you going to control the aircraft? With no hydraulics, you have no flight controls!


FALSE.
A 737 will fly all day long with failed hydraulics.
Granted, you’ll want to use STBY RUDDER pumps.
But you speak as though the loss of hydraulics will crash a plane. And in many cases, it won’t. Redundancy on most airplanes, and manual reversion on planes like the 737.

Regarding United 232, I fail to see what difference flap position would have made on that outcome.


REALLY? Care to explain how what I am posting is false? The 737 has manual reversion, just like the 727. If you lose hydraulics you still have cables. On ALL models of the 747, if you lose hydraulics, you also lose flight controls. So, all hydraulic failure, you are merely a passenger. If you know differently, I'd love to know.


This is correct. Unfortunately, if you lose all hydraulics on the 747, there is no manual reversion for primary flight controls….
 
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dennypayne
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Re: Can 747s really use flaps even with total hydraulic loss and if so why isnt this on other aircraft?

Tue Nov 23, 2021 4:58 pm

AA737-823 wrote:
Regarding United 232, I fail to see what difference flap position would have made on that outcome.


I agree it likely wouldn’t have made a major difference. IIRC they “landed” at around 200 knots, and a slower speed may have improved survivability - hard to know though. Whether it would have been wise to lower flaps and further experiment with the controllability issues they were having is another matter.
 
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tb727
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Re: Can 747s really use flaps even with total hydraulic loss and if so why isnt this on other aircraft?

Tue Nov 23, 2021 6:25 pm

Kindanew wrote:
The A380 and A350 are also flyable with a total hydraulics loss as well I believe.


I will speak for the narrow body Airbus, it is "flyable" with a total hydraulic loss, not sure if it's going to be land-able. There is a mechanical backup for the rudder and THS. I heard recently in the school house that mechanical back up of the rudder will be going away at some point soon in the new build A320Neo series.

No alternate flaps either on the A320 series. We recently added a No Flap landing to our recurrent sims, I hadn't done one since my type ride about seven or so years ago. It was pretty easy, first try no problem at all, you're just landing fast and make sure you pick a long runway. I want to say the weight was 135,000 pounds, which is 10,000 under max, and 16L in SEA was more than enough.
 
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glen
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Re: Can 747s really use flaps even with total hydraulic loss and if so why isnt this on other aircraft?

Tue Nov 23, 2021 6:51 pm

tb727 wrote:
I will speak for the narrow body Airbus, it is "flyable" with a total hydraulic loss, not sure if it's going to be land-able. There is a mechanical backup for the rudder and THS. I heard recently in the school house that mechanical back up of the rudder will be going away at some point soon in the new build A320Neo series.

The mechanical backup is unusable if you loose all hydraulics. Mechanical backup means the hydraulic motors which drive the screw jack for the stabiliser are controlled by the mechanical trim wheel instead by one of the three electric motors, but you still need the hydraulics.
Same for the rudder: Even if you control the rudder mechanically via the pedals, the rudder itself is still actuated by hydraulic motors.
 
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Starlionblue
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Re: Can 747s really use flaps even with total hydraulic loss and if so why isnt this on other aircraft?

Wed Nov 24, 2021 1:02 am

Kindanew wrote:
The A380 and A350 are also flyable with a total hydraulics loss as well I believe.


That depends on how you define hydraulics.

The A350 has two "traditional" hydraulic systems. However, it also has some self-contained hydraulic actuators. If you lose the two hydraulic systems, you can still fly with the self-contained actuators. They're still hydraulic though, so have you really lost all hydraulics? ;)
 
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jetmech
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Re: Can 747s really use flaps even with total hydraulic loss and if so why isnt this on other aircraft?

Thu Nov 25, 2021 10:12 am

VMCA787 wrote:
With no hydraulics, you have no flight controls!

Just to add to the topic in general, the 747 flaps are powered by two of the four hydraulic systems only, with #1 powering inboard flaps and #4 powering outboard flaps. Thus, any issues associated with alternate flap extension (i.e. extended transit time) will be there even without total hydraulic loss. But certainly, as you mention, total hydraulic loss would be the overarching issue!

Regards, JetMech
 
seven47
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Re: Can 747s really use flaps even with total hydraulic loss and if so why isnt this on other aircraft?

Thu Nov 25, 2021 9:44 pm

jetmech wrote:
VMCA787 wrote:
With no hydraulics, you have no flight controls!

Just to add to the topic in general, the 747 flaps are powered by two of the four hydraulic systems only, with #1 powering inboard flaps and #4 powering outboard flaps. Thus, any issues associated with alternate flap extension (i.e. extended transit time) will be there even without total hydraulic loss. But certainly, as you mention, total hydraulic loss would be the overarching issue!

Regards, JetMech


I agree with all of the above. I flew post-maintenance test flights in the 747-100/‐200 for a number of years, and many of those fights required alternately extending and retracting the leading- and trailing edge flaps. They take a long time to transit to the selected position!
 
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jetmech
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Re: Can 747s really use flaps even with total hydraulic loss and if so why isnt this on other aircraft?

Thu Nov 25, 2021 10:44 pm

seven47 wrote:
They take a long time to transit to the selected position!

We used to extend flaps in the hangar on alternate power for that exact reason.

Regards, JetMech

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