19AB67

We love it! Krueger flaps retract during reverse thrust

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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! 

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

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Yup, I thought so. 

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

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16 hours ago, MarkW said:

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

You're right, they did.

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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.

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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.

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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

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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).

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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.

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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.

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Um, how to make this visible? 

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

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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! 

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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!

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23 minutes ago, skelsey said:

the flap position indicator goes from green to magenta

Now, I got it. Thanx.

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This was one of many modifications to make the thrust reverser system safer. The reverser system uses several microswitches in the thrust quadrant which activate sequentially as the reverse levers are lifted. There was a previous incident where a pilot placed a manual forward of the thrust quadrant prior to takeoff. When the forward thrust levers advanced, the reverse levers contacted the manual triggering the first part of reverser operation. The trigger point was subsequently changed. I have a vague recollection that BA was involved with this one, too (???) :laugh:

There was that terrible accident with Lauda Airlines (B767) where the reversers deployed in flight. Note that 767 engines can be fitted to 747s. This resulted in one of the first reverser modifications.

Cheers

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16 hours ago, Qavion2 said:

There was that terrible accident with Lauda Airlines (B767) where the reversers deployed in flight. Note that 767 engines can be fitted to 747s. This resulted in one of the first reverser modifications.

Cheers

This shouldn't happen on the B744, because the reversers can only be deployed on the ground and with the engines running.  There is also an interlock mechanism which mechanically prevents simultaneous movement of the forward and reverse thrust levers, so that each reverse thrust lever can only be raised when the relevant engine's forward thrust lever is in the closed position.

There can occassionally  be a slight lag between each engine's interlock releasing and this can initially prevent all four reverse thrust levers being raised simultaneously.  In this case it usually pays to pause for a second or two after raising the reverse thrust levers before applying reverse thrust. On a non-limiting runway then either idle reverse or partial reverse (approx 70% N1) may be used.    

If a fault is detected in the reverser system then the EICAS message  "ENG REV LIMTD" or "ENG REVERSER" will be displayed . The "...LIMTD" message means that only reverse idle will be available after landing on the affected engine.  However, "ENG REVERSER" is probably the most serious because if another fault is detected in that reverser system then there is a risk that it could inadvertently deploy in flight.

Regards,

Bertie Goddard

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2 hours ago, berts said:

This shouldn't happen on the B744, because the reversers can only be deployed on the ground and with the engines running.

Was this not the case on the 767?

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1 hour ago, Captain Kevin said:

Was this not the case on the 767?

I can't answer this for certain because I am not familiar with the B767.  However, I would be rather surprised if Boeing's reverser logic wasn't similar for the same engine type (i.e.. RR, P&W or GE).

Bertie Goddard 

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16 minutes ago, berts said:

I can't answer this for certain because I am not familiar with the B767.  However, I would be rather surprised if Boeing's reverser logic wasn't similar for the same engine type (i.e.. RR, P&W or GE).

I would have figured this would have been the case on the 767, but your comment saying that this shouldn't happen on the 747-400 threw me off because I assumed the same would be said for the 767, yet there was the Lauda Air 767 where the reverser did deploy in flight.

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14 hours ago, berts said:

This shouldn't happen on the B744, because the reversers can only be deployed on the ground and with the engines running.

I can assure you the engines don't need to be running. I've done it many times :wink: However to go past idle reverse, you do need the engine EECs powered (which can be done by various methods).

The 767 has the same safeguards as the 747. However, if something in the reverser system is telling you that the aircraft is doing something it actually isn't, then you will get things to happen which shouldn't happen. In theory, you shouldn't be able to move the reversers without pneumatic power, but I've heard a few tales from fellow engineers who said the reversers have moved with pnematics off (We believe it's due to trapped air pressure in the system).... and I've slapped at least one apprentice's hands for attempting to move the levers (because he thought it was safe)

Hope this makes sense

Cheers

JHW

 

P.S. By the way, I haven't tried this in v3, but you should be able to activate a reverser on the ground using APU air, if you pull a start switch (with the Autostart switch ON).. then pull on the respective reverse lever (It's an old engineer's trick)

 

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11 hours ago, Captain Kevin said:

I would have figured this would have been the case on the 767, but your comment saying that this shouldn't happen on the 747-400 threw me off because I assumed the same would be said for the 767, yet there was the Lauda Air 767 where the reverser did deploy in flight.

An additional locking mechanism was added to the reverser after the Lauda Air accident.

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Gents,

I love seeing you guys get into discussion of minute details- because most of them are present here.

For anyone interested- during reverse, glance down at your flap position indicator.  It changes to show the condition- but it takes a practiced eye to see and understand what you are observing...

 

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1 hour ago, rsrandazzo said:

For anyone interested- during reverse, glance down at your flap position indicator.  It changes to show the condition- but it takes a practiced eye to see and understand what you are observing...

Yeah, I did that shortly after I read one of the posts. You certainly wouldn't necessarily notice it on landing as you'd be focused on....WEL....landing.

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