Bleed air sources

[dutch57]

Hardy Jeroen, goodevening

I can not think of a scenario where duct pressure is lost and returns just because you operate the Le flaps  in real time.

Remember you have 4 engines delivering air to the pneumatic system , you have lh/rh isolation vlv`s. even if the cross-over duct fails you can isolate that.

Eng duct failures close the PRSOV or isolate the wing.

What i would like to say is try to look at it this way , primary power for the Le-flaps is the pneumatic system.

And the pneumatic system has a few possible sources to get the air.

sincerly Bob

[dutch57]

Hardy goodafternoon,

About the PRSOV , normal operation is eng duct pressure as muzle pressure to open-regulate-close the vlv.

When you have reverse flow , the vlv closes and stays closed as long as the reverse flow condition excists(leaving the bleed switch in on)

Exception is during engine start reverse flow protection is inhibited  and muzle pressure to open the vlv comes from the pneumatic system. Also a close signal is send to the PRV controller to keep the PRV closed until the eng reaches 50%n2
After engine start the bleed system will follow the normal bleed skedule

Hope this sheds some more light into the eng bleed system and interaction with the pneumatic system.

sincerly,
Bob

[Hardy Heinlin]

Perfect. This agrees with my model.

Now I just wonder if reverser sleeve operation requires bleed air only during sleeve motion or as long as the sleeves are deployed.

(By the way, does anybody know if the EICAS flap lever turns magenta when the LE flaps are auto-retracted by the thrust reverser logic?)

Thanks!


Cheers,

|-|ardy

[Avi]

I read a manual I have and here is something I found:

Pneumatic ground power carts may not be capable of supplying
sufficient air (3000 CFM and 15 psi minimum) to operate all the
LE flaps simultaneously.

[dutch57]

Hardy, goodevening

The bleed air needed for reverse operation is via a T/R prsov which will open for a deploy command  and closes when the reverser is deployed.

It will open again when it gets a stow command and closes when the reverser is in stow.

sincerly Bob

[dutch57]

Hardy,

I feel it will stay green as the logic for turning magenta is when a flap is not in its commanded position.

as group A is commanded to retract during reverse thurst operation. The Le-flaps are in their commanded position therefore (i feel) the the indication will be green during reverse operation.

I the case a Le-unit fails or set fails it will turn into magenta as this is a non-normal situation during reverse

sincerly,
Bob

[Hardy Heinlin]

I feel what you feel :-)

But I wanted to be sure. It obviously depends on the definition of the word "commanded". Aside from the flap lever command, it may also include ...

... thrust reverse logic commands(?)

... flap relief commands(?)


Cheers,

|-|ardy

[John H Watson]

Also a close signal is send to the PRV controller to keep the PRV closed until the eng reaches 50%n2
After engine start the bleed system will follow the normal bleed skedule

Just some additional info:

Normal ops won't resume until 15 seconds after the Start Valve has completely closed. The PRV (or FWSOV) is commanded closed whenever the Start Valve is open. Start Valve position is monitored by the ASCTU and the ASCTU controls the PRV (or FWSOV)

Rgds
JHW

P.S. I can't say I've noticed, but I suspect the Bleed OFF light would illuminate for 15 seconds after the start valve re-closed(?)

[dutch57]

Hardy,

If you mean flap load relief, if that happen it will turn magenta, i see that during tests in the hanger we test the system on a regular basis.

sincerly,
Bob

[John H Watson]

If this is the indication for Flap Load Relief, then why should it not be the same for reverser operation?

In your hangar tests, does the magenta appear only when the flaps are in transit to/from the Flap Load Relief position, or whenever there is a disagreement between lever and flaps?

Rgds
JHW

[dutch57]

John,

Flap load relief is a non-normal condition and when it happens the system retracts the flaps, the green will turn magenta with an eicas warning.
As soon as the Te-flaps retract the colour changes.

Le-flaps retracting, during reverse thrust is a normal condition therefore no change in indication.

[John H Watson]

As soon as the Te-flaps retract the colour changes.

Bob, are you saying that when the flaps reach the flap load position that they change back to green? Or are you saying that when they begin to move to the flap load position that they change from green to magenta and stay magenta?

[dutch57]

John,

Flaps 30 green, load relief starts, Te flaps start to move to 25 units, magenta and stay magenta unil return to 30 units..

Bob

[John H Watson]

Thanks, Bob.

I still don't understand why Boeing chose this indication logic. The FCU is commanding flaps 25, the Flap Input Actuator is moving to 25 and the flaps are moving to 25.

The magenta flap lever marker seems to be triggered by a variety of factors, some not related to flap lever Vs flap position.

Rgds
JHW

[dutch57]

John,

Yes you are right the marker is triggered by various factors.

But basicly you can say normal situation and non-normal situation

A flap load relief command is a non-normal hence the magenta because your flap lever remains in 30 units.

If you move your flap lever to the 25 position after the load relief retracted the flaps there , the marker will turn back to green , since the load relief need is removed and you return in a normal situation.

But keep in mind a load relief will occur during finals and the crew has a hight workload so they will not move the flap lever, and i doubt if thet notice the change of colour from the marker.

I saw a few times during app flaps 30 on final the marker changes colour , reason a critical adjusted flap position x-mtr
Crew did not notice they were flying the plane for landing

Sincerly Bob

Ps, warning logis and eicas indications can vary between operators as the are pin programmed via the EIU`s