777 Tail strike...Hkg

[Homerun]

There is thread on FlyerTalk with an account from a pax onboard.  He claims they hit 3 times...I’m guessing there were a couple bounces

[boestar]

Airplanes bend.... Ever ridden in the back of a stretched DC-8???  you can lose sight of the cockpit door from the back just from it wagging its tail.  A high G impact will distort the fuselage in al kinds of ways.  This may be one.   The skid may have hit but the belly did too.

[blues deville]

A Boeing friend has reminded me that although the tail skid may save the aircraft from serious damage during landings, it’s main function is protection on take off. If you damage the tail during landing it’s probabaly going to require a repair but it’s safely on the ground. A take off event might be more critical with fuselage and structural issues. Boeing has had tail skids on their planes since the (photo) B29. 

[blues deville]

13 hours ago, Kip Powick said:

I find it hard to get my mind around the fact that if it was a tail strike, how did the fuselage get scraped so far ahead of the skid ??

Why was there no photos of where there was impact on the runway, surely there would be a paint smudge on the runway but no forum mentions that anything was found on the runway.

Is it possible that the aircraft fuselage touched something on approach prior to landing??

Going to be an interesting investigation/conclusion.....

I think it’s just the combined nose high attitude and MLG compressed allowing that bend in the fuselage to make contact. Flex in the aft fuselage may also be a factor. Boeing clearly provides the numbers to be respected at all times. 

 

[Kip Powick]

Well is sure would have to be a BIG bend in the fuselage that would allow the fuselage to hit prior to the skid.

[mrlupin]

That aircraft has the tail skid... Boeing has taken it off the latest models. You have to wonder to what effect. Even within the AC fleet, the later models do not have the tail skid.

 

 

[blues deville]

1 minute ago, Kip Powick said:

Well is sure would have to be a BIG bend in the fuselage that would allow the fuselage to hit prior to the skid.

But that’s my point Kip. The tail skid won’t protect all conditions. The -300ER geometry of 8 degrees NU and MLG fully compressed results in zero clearance at the sensor which is located at the lowest point on the bend. The tail skid won’t intervene. 

On take off, a faster than normal rotation with the main gear off the ground and the nose continuing up can result in a tail skid only contact reducing the impact to the tail structure.

[blues deville]

12 minutes ago, mrlupin said:

That aircraft has the tail skid... Boeing has taken it off the latest models. You have to wonder to what effect. Even within the AC fleet, the later models do not have the tail skid.

 

 

It’s a weight saving, maintenance free feature. The tail strike protection system is part of the flight control input. Designed by a team of five engineers at Boeing.

[boestar]

if thats the case then that should be considered a design flaw.  The line from the fullly compressed gear to the tail skid should have no impact on any structure in between.  I am not sure if that takes into account flat tires.  The point being that at the minimum unstick speed you can rotate the aircraft with the Mains still on the ground and drag the tail skid until the aircraft lifts off.  This is a certification test.

As for the bend it does not need to be a bend so much as a deformation of the cylinder to an oval shape to cause the impact.

 

[blues deville]

1 minute ago, boestar said:

if thats the case then that should be considered a design flaw.  The line from the fullly compressed gear to the tail skid should have no impact on any structure in between.  I am not sure if that takes into account flat tires.  The point being that at the minimum unstick speed you can rotate the aircraft with the Mains still on the ground and drag the tail skid until the aircraft lifts off.  This is a certification test.

As for the bend it does not need to be a bend so much as a deformation of the cylinder to an oval shape to cause the impact.

 

Not a design flaw but an operational limitation as are many others on the 777 and all aircraft. Some carriers consider the takeoff and landing attitude limits to be memory items. 

[boestar]

the point being that fuselage impact should not be possible based on the geometry.  The straight like from the Main Wheel to the tail skid should not intersect any other part of the fuselage.

if you rotate at the minimum speed all the way to strike then the only damage should be on the skid plate on the bottom of the skid.  

[blues deville]

15 minutes ago, boestar said:

the point being that fuselage impact should not be possible based on the geometry.  The straight like from the Main Wheel to the tail skid should not intersect any other part of the fuselage.

if you rotate at the minimum speed all the way to strike then the only damage should be on the skid plate on the bottom of the skid.  

You may have seen worse but here’s some on 737’s. Continually  stretching airliners such a the DC8, B737, 777, Dash 8 etc. creates pilot operational limitations. In the case of the 777 the tail skid obviously won’t protect all conditions. Boeing provides the operators with this information. 

[Kip Powick]

42 minutes ago, blues deville said:

But that’s my point Kip. The tail skid won’t protect all conditions. The -300ER geometry of 8 degrees NU and MLG fully compressed results in zero clearance at the sensor which is located at the lowest point on the bend. The tail skid won’t intervene. 

On take off, a faster than normal rotation with the main gear off the ground and the nose continuing up can result in a tail skid only contact reducing the impact to the tail structure.

OK..I have looked at the video of the 777 taking off and I can see a point where if the aircraft was landing and it was a HARD landing the fuselage ahead of the skid would hit the runway and the skid would not.

You mentioned sensor...Did this aircraft have a sensor?? I thought only the newer models deleted the tail skid for the electronic means of warning the crew of  possible/pending tail strike.

Regardless I still have a problem with the fuselage bending so much that it hits the runway on the flare...it must be one big HARD landing for the fuselage to hit the runway, almost a vertical "crunch".

Bit off topic but doesn't Hong Kong have a video of every landing?? NRT does. 

[DEFCON]

Blues - I think the gear on the 777 aircraft is an impressive piece of engineering too.

 

High attitude doesn't work.

If a vertical deceleration results in full compression of the oleos, but there's still loads of G to unload, things are going to bend.

 

[ckl]

 

With compressed tires and oleos fully compressed not difficult to see why fuselage hit. I always thought the tailskid was designed to protect the aircraft during T/O only.

[boestar]

The tail skid doesnt actually "protect" anything.  It is a tell tale as to weather you hit or not.

Maintenance has an inspection item for the tail skid on many aircraft.  Evidence of a tail strik triggers further inspection components.

We had an inspection many moons ago on the tristar.  There was lockwire threaded in a triangle (go figure) over the tail skid.  if it was broken or "shaved" then there was an inspection to be done.  on one inspection the lickwire was gone, the skid was flat and the bulkhead to which it was attached was buckled.  as you can imagine this triggered much more extensive inspection and one large repair.

Notice in the picture above the oleo is compressed and the tail skid is in contact.  The belly is not.  it wont take many Gs to make the belly scrape.

FWIW some aircraft have a compression cylinder that crushes under specific loading.  The 727 comes to mind.  When checked the amount of compression indicates the severity of the tail strike.  Fully compressed would also show damage on the belly from contact.

 

[blues deville]

I would think

2 hours ago, boestar said:

The tail skid doesnt actually "protect" anything.  It is a tell tale as to weather you hit or not.

Depending on the event I would think it can potentially save millions of dollars in damage to an aircraft. 

[boestar]

Well Not really.  I have see 2 incidents in my career where the tail skid has torn up the structure of the aircraft.  One was the aforementioned L-1011 and the other a 727-200.

While the Skid does serve as a buffer during a strike event it will not overcome and prevent more damage.   The tail skid by design is meant to compress as both an indication and a gauge to an event.    Of course not all aircraft are created equal and some smaller aircraft simply have a "skid Plate"

As I mentioned above the AMM has specific requirements if the Tail skid has any indication of contact with the surface.  It matters not if the pilot noticed or reported it.  The AME will find it.

 

[blues deville]

1 hour ago, boestar said:

Well Not really.  I have see 2 incidents in my career where the tail skid has torn up the structure of the aircraft.  One was the aforementioned L-1011 and the other a 727-200.

While the Skid does serve as a buffer during a strike event it will not overcome and prevent more damage.   The tail skid by design is meant to compress as both an indication and a gauge to an event.    Of course not all aircraft are created equal and some smaller aircraft simply have a "skid Plate"

As I mentioned above the AMM has specific requirements if the Tail skid has any indication of contact with the surface.  It matters not if the pilot noticed or reported it.  The AME will find it.

 

[Maverick]

Well, if western manufacturers just took a cue or two from the Russians, tail-strikes would not be a problem!

 

[J.O.]

That's pretty funny. With the main gear so far aft, you'd need to work pretty hard to tail strike an IL-62.

[deicer]

2 hours ago, Maverick said:

Well, if western manufacturers just took a cue or two from the Russians, tail-strikes would not be a problem!

 

The IL-62 'pogo' was used when taxiing and on the gate to hold the nose on the ground. Not for air ops. Until it was fueled, and the front hold loaded, it was massively tail heavy. Much like the 727 and having to have the tail stair down to keep it from tipping.   Saw LOT aim for the sky in YYZ once when the ground electrics were pulled before the apu was started.  Good thing the paymover was hooked up, the towbar kept it from contacting the ground and actually causing damage.  Was rectified by getting a ladder, rehooking the electrics, setting the parking break and pulling forward until the nose was on the ground again.  Ah the good old days....

[blues deville]

Post from another site:

Dec 12

 

Replying to

@TomPodolec

@AirCanada

and

@flightradar24

I was on this flight! Very unusual pitching and rolling as we approached runway, nothing like I've ever experienced. Landing so hard that overhead bins opened and bags fell out (bruise on my arm to show for it) plus we had a bounce. Pilot came on and said turbulence

[rudder]

Assuming things happened as described (or hypothetically) would recovery from a bounced landing not be to execute a go-around (of course presuming T/R was not selected)?

The previously posted video of landings at NRT(?) in heavy winds includes a bounced 787 landing/no go around. Not pretty.

I am not sure that being in such a low energy state and above the runway will not lead to aircraft attitudes or descent rates that may result in excessive g loading on touchdown by parts of the aircraft not designed for such loading (think aft fuselage or nosewheel if recovery included aggressive forward pitch input).

[Canoehead]

On 12/16/2018 at 11:48 AM, conehead said:

So.... what’s the “G” number rumour floating about?

Hi conehead.  I only heard this second hand, but north of 3.