We love it! Krueger flaps retract during reverse thrust

[19AB67 16]

Folks, 

have you ever noticed that after touch down and reversers open the inboard and central leading edge Krueger flaps retract, but not the outer ones? 

I have seen that first time in some YouTube 747 landing videos. 

Of course we are all fully concentrated during our own landings keeping the bird centre-line to watch this happening, 

but check it out! 

[MarkW 1,491]

They did this on the original release as well (I think).

[Marc320 2]

It retract to avoid damage due to reverse airflow .

 

Marc Delaloy

[19AB67 16]

Yup, I thought so. 

However, haven't found it yet described in the FCOM. 

[craig_read 43]

16 hours ago, MarkW said:

They did this on the original release as well (I think).

You're right, they did.

[Captain Kevin 586]

5 hours ago, 19AB67 said:

However, haven't found it yet described in the FCOM. 

Probably not something the pilots would really need to know when it comes to flying the plane since it probably won't really alter the handling characteristics of the plane at that point.

[skelsey 765]

7 hours ago, 19AB67 said:

However, haven't found it yet described in the FCOM. 

9.20.15 in mine (not sure about the one supplied by PMDG):

Quote

During engine reverse thrust operation, automatic retraction of inboard and midspan leading edge flaps changes the flap position indicator to reflect flaps intransit.

 

2 hours ago, Captain Kevin said:

Probably not something the pilots would really need to know when it comes to flying the plane since it probably won't really alter the handling characteristics of the plane at that point.

However, very relevant to know in the event of a reverser fault: this led to a very alarming situation at Joburg back in 2009.

I seem to recall there has since been a modification as a result to mitigate against this, though I can't recall the details offhand at the moment.

[19AB67 16]

4 hours ago, skelsey said:

Quote

During engine reverse thrust operation, automatic retraction of inboard and midspan leading edge flaps changes the flap position indicator to reflect flaps intransit.

 

Right, there it is mentioned. 

I think the sentence itself refers to the altenate flap indications. 

Just flying 5X58 PHNL to PGUM. I will land with alternate flaps!    8^D

[Captain Kevin 586]

9 hours ago, skelsey said:

However, very relevant to know in the event of a reverser fault: this led to a very alarming situation at Joburg back in 2009.

Fair enough. Was not aware that that actually happened.

[Qavion2 39]

16 hours ago, skelsey said:

I seem to recall there has since been a modification as a result to mitigate against this, though I can't recall the details offhand at the moment.

A small wiring modification.

When the rev thrust levers are physically moved to 10 degrees, a signal is sent to the Flap Control Units. Prior to the modification, the LE flaps were activated by the reverser stowed/unstowed position indication system (which has been troublesome in the past).

[Boomer 1,619]

On 2017-04-21 at 1:57 PM, MarkW said:

They did this on the original release as well (I think).

ha!  I have the 744x for FSX installed andso will now go see.

[Captain_Al 66]

On 4/22/2017 at 4:08 PM, 19AB67 said:

Right, there it is mentioned. 

I think the sentence itself refers to the altenate flap indications. 

Just flying 5X58 PHNL to PGUM. I will land with alternate flaps!    8^D

This is referring to the Flaps in the primary mode. Because part of the inboards retract on landing with reverse, the position indicator changes from green to magenta during the rollout. Not really something you are looking at while maintaining directional control and making landing call outs.

[19AB67 16]

Um, how to make this visible? 

Usually we see only the combined Krueger/flap indication... 

[skelsey 765]

6 minutes ago, 19AB67 said:

Um, how to make this visible? 

Usually we see only the combined Krueger/flap indication... 

I'm not sure what you mean...

As Al says, the flap position indicator goes from green (indicating all TE and LE devices are in the commanded position) to magenta (because the inboard LE flaps are/have retracted and therefore the configuration does not technically match the flap lever position) when you select reverse thrust. This happens on every landing, but you probably haven't noticed it because, as Al says, your attention is most likely elsewhere! 

[skelsey 765]

On 23/04/2017 at 11:12 AM, Qavion2 said:

A small wiring modification.

When the rev thrust levers are physically moved to 10 degrees, a signal is sent to the Flap Control Units. Prior to the modification, the LE flaps were activated by the reverser stowed/unstowed position indication system (which has been troublesome in the past).

Thanks John - I knew I could count on you!