Hypothetical Scenario #1 - Urgent Action required

This is a voluntary pop quiz.

You're circling in a 30 degree left bank at 3000 AGL.

You hear a thunk and the glider enters a spin. Your practiced spin recovery technique does not work in the usual amount of time. You look in the direction of the thunk and see that the left spoiler is full open, you confirm that the spoiler control handle is in the fully closed position. A quick look confirms that the right spoiler is full closed.

What do you do next? Why did the left spoiler pop open. What just happened?

To derive the full benefit of this exercise, you might respond to this thread with your answer before looking at any of the other replies.

My hypothetical solution and explanation follows as the next comment.

First of all if it is a spoiler as on early Schweizer gliders it would be blown to the closed position.

If the drag devices you speak of are actually air brakes, as they are likely named in the POH, you have a problem.

This confusion can be deadly.

Robert Mudd
CFIA-G

On Wednesday, February 5, 2014 9:19:04 PM UTC-7, OneTango wrote:
You look in the direction of the thunk and see that the left spoiler is full open, you confirm that the spoiler control handle is in the fully closed position. A quick look confirms that the right spoiler is full closed.



What do you do next? Why did the left spoiler pop open. What just happened?



To derive the full benefit of this exercise, you might respond to this thread with your answer before looking at any of the other replies.



My hypothetical solution and explanation follows as the next comment.

This is my best guess. I have no idea if it is correct.

What do you do next?

Use the spoiler handle to open the right spoiler to match the left.

Follow my practiced spin recovery technique and return to level flight with both spoilers fully open.

Decide whether to land or bail out.

If there is a place that I can land with both spoilers fully open. Do that..

If I cannot make it to a field with both spoilers open, quickly determine if it is possible (and if there is less sink) to fly with one spoiler open and one spoiler closed. If it is possible, decide whether to try it or bail out.

Why did the left spoiler pop open?

When the push rod that controls the spoilers locks past the detente, it is under compression and it is designed to bend slightly. Due to a manufacturing defect, the bent aluminum push rod rubs against the fiberglass where it passes through a wing rib (hole is not in exactly the right place or hole is not the right shape or size). Over time, the glass wing rib saws through the aluminum pushrod. At a certain point the pushrod buckles and breaks. The spoiler pops open.

On Wednesday, February 5, 2014 8:42:13 PM UTC-8, OneTango wrote:
This is my best guess. I have no idea if it is correct.



What do you do next?



Use the spoiler handle to open the right spoiler to match the left.



Follow my practiced spin recovery technique and return to level flight with both spoilers fully open.



Decide whether to land or bail out.



If there is a place that I can land with both spoilers fully open. Do that.



If I cannot make it to a field with both spoilers open, quickly determine if it is possible (and if there is less sink) to fly with one spoiler open and one spoiler closed. If it is possible, decide whether to try it or bail out.



Why did the left spoiler pop open?



When the push rod that controls the spoilers locks past the detente, it is under compression and it is designed to bend slightly. Due to a manufacturing defect, the bent aluminum push rod rubs against the fiberglass where it passes through a wing rib (hole is not in exactly the right place or hole is not the right shape or size). Over time, the glass wing rib saws through the aluminum pushrod. At a certain point the pushrod buckles and breaks.. The spoiler pops open.

Your scenario #1 actually did happen in a DG-400 at Truckee about 25 years ago. One spoiler needed to be adjusted slightly, so the (non mechanic) pilot gave the quick disconnect fitting a half turn in. Under positive G force the fitting was now trying to pull away from the ball, rather than being forced into to ball. At about 4000 feet AGL, one spoiler popped full open. The pilot correctly assessed the situation and pulled the other spoiler open. Having plenty of altitude, he decided to enter the pattern to the normal glider runway (19) at 2000 feet..........thinking that extra altitude is always good, right? The extra altitude meant he had to fly farter down-wind to get rid of his excess altitude, turned final into some wind and didn't make it back to the runway! Landing short of 19 at Truckee means you hit a cliff.

If you are faced with this situation (one spoiler open), Put the ship in the middle of the longest runway available!
JJ

Similar failure happened on a Nimbus 4DM some years ago - on a fast
final glide into Gariep.

Height was low, speed was high (well past Vmo) when they hit a powerful
thermal.
Wings took the shock, but one airbrake actuator failed under the shock
load. It had been damaged by "buzzing" over an extended period - the
caps were not held down properlyso the blade would chatter in it's box
on pull ups. This set up fatigue in the connecting rod which snapped
under the sudden whip motion on the wing.

Due to high speed, no spin departure.
The resulting yaw caused an immediate roll toward the open brake wing.
Pilot correctly assessed the situation, opened the other airbrake and
attempted to recover from the inadvertent barrel roll.
Attempt was unsuccessful, wings failed symmetrically at the outer panel
join, and then a couple of metres from the root - conveniently
preserving the failed actuator and the witness marks... Calculated
failure somewhere on the far side of 300km/h and enormous g.

Fuselage impact was a couple of seconds later - both pilots being
ejected many metres from the point of impact.
Being a DM the resulting fire destroyed much of the confetti that
remained. Somehow, enough of one of the three loggers remained for a
trace to be obtained.

Moral of that story is - check your airbrake actuators for wear and
fatigue - particularly on long flexible wings. And have some respect for
the numbers - they are there for a reason.

Time from initial failure to impact was maybe 30s. Think about how fast
you can close the distance to the ground next time you are at 250km/h
and 600 feet height.
That height is the distance you are travelling in three seconds (70m/s).

Bruce


On 2014/02/06 4:02 PM, JJ Sinclair wrote:
On Wednesday, February 5, 2014 8:42:13 PM UTC-8, OneTango wrote:
This is my best guess. I have no idea if it is correct.



What do you do next?



Use the spoiler handle to open the right spoiler to match the left.



Follow my practiced spin recovery technique and return to level flight with both spoilers fully open.



Decide whether to land or bail out.



If there is a place that I can land with both spoilers fully open. Do that.



If I cannot make it to a field with both spoilers open, quickly determine if it is possible (and if there is less sink) to fly with one spoiler open and one spoiler closed. If it is possible, decide whether to try it or bail out.



Why did the left spoiler pop open?



When the push rod that controls the spoilers locks past the detente, it is under compression and it is designed to bend slightly. Due to a manufacturing defect, the bent aluminum push rod rubs against the fiberglass where it passes through a wing rib (hole is not in exactly the right place or hole is not the right shape or size). Over time, the glass wing rib saws through the aluminum pushrod. At a certain point the pushrod buckles and breaks. The spoiler pops open.

Your scenario #1 actually did happen in a DG-400 at Truckee about 25 years ago. One spoiler needed to be adjusted slightly, so the (non mechanic) pilot gave the quick disconnect fitting a half turn in. Under positive G force the fitting was now trying to pull away from the ball, rather than being forced into to ball. At about 4000 feet AGL, one spoiler popped full open. The pilot correctly assessed the situation and pulled the other spoiler open. Having plenty of altitude, he decided to enter the pattern to the normal glider runway (19) at 2000 feet..........thinking that extra altitude is always good, right? The extra altitude meant he had to fly farter down-wind to get rid of his excess altitude, turned final into some wind and didn't make it back to the runway! Landing short of 19 at Truckee means you hit a cliff.

If you are faced with this situation (one spoiler open), Put the ship in the middle of the longest runway available!
JJ


--
Bruce Greeff
T59D #1771

On Saturday, February 8, 2014 12:35:58 PM UTC-8, BruceGreeff wrote:
Similar failure happened on a Nimbus 4DM some years ago - on a fast

final glide into Gariep.



Height was low, speed was high (well past Vmo) when they hit a powerful

thermal.

Wings took the shock, but one airbrake actuator failed under the shock

load. It had been damaged by "buzzing" over an extended period - the

caps were not held down properlyso the blade would chatter in it's box

on pull ups. This set up fatigue in the connecting rod which snapped

under the sudden whip motion on the wing.



Due to high speed, no spin departure.

The resulting yaw caused an immediate roll toward the open brake wing.

Pilot correctly assessed the situation, opened the other airbrake and

attempted to recover from the inadvertent barrel roll.

Attempt was unsuccessful, wings failed symmetrically at the outer panel

join, and then a couple of metres from the root - conveniently

preserving the failed actuator and the witness marks... Calculated

failure somewhere on the far side of 300km/h and enormous g.



Fuselage impact was a couple of seconds later - both pilots being

ejected many metres from the point of impact.

Being a DM the resulting fire destroyed much of the confetti that

remained. Somehow, enough of one of the three loggers remained for a

trace to be obtained.



Moral of that story is - check your airbrake actuators for wear and

fatigue - particularly on long flexible wings. And have some respect for

the numbers - they are there for a reason.

Very interesting report, we had a Nimbus 4DM come apart at Minden and both pilots were killed several years back. They got into a death spiral for unknown reasons..............wonder if one spoiler could have popped open to start the spiral? The accident report stated that both spoilers deployed when the ship was near vertical, but now I'm wondering if one was open before the other? I have seen instances where one spoiler came out caused by bending of its pushrod or flexing of drive unit in the root rib, but nothing broke! Would the accident investigator notice a bent rod or flexed root rib in a pile of fiberglass rubble?
JJ

In one of the early replies, One Tango mentioned the bending of the pushrod and rubbing on the fibreglass "rib." I have seen this but rather than a rib, it was the opening into the spoiler boxes on an SZD Junior. The thin fibreglass of the opening was rubbing on the pushrod and sawing through it like a hacksaw. It was happening primarily on one wing with the other side just starting to leave a mark. We discovered it because there was a problem with this aircraft where one spoiler would open at a slightly before the other so we tried adjusting it to get them to open and close at the same time as well as open to the same height. We started this process because the spoilers did not seem to want to stay locked and as we tested it noticed they were not actuating at the same time. Adjustment required removal of the pushrods and that was when we found it. A review of the logbooks showed that the aircraft had an accident early in its life and one wing was replaced with a brand new one. As the investigation continued, we also found that the pushrod actuating gears were "crunchy" on the original wing but smooth on the other new wing and when we pulled it out of the wing (not an easy task but can be done through an opening in the root rib) we could find no damage but they did not feel right. These gears do not have bearings so the initial thought was not the problem. I was able to discover online that there was a fatality when a Junior spun in after one spoiler opened. The conclusion was that the teeth on the nylon-like gears had sheared off. It may be that the tolerances were such that they did not mesh properly or it was a material fault. We decided to order a new gear set along with the a replacement pushrod. However, none of this explained the differing operation of the spoilers that was the cause of our initial investigation. In the end, we figured out that when the wing was replaced, the fittings had been improperly installed in the torque tube in the fuselage. Accuracy is very important. When a wing is replaced, the collars that are installed on the torque tube do not come predrilled. You have to fit the wing, mark the place where the holes are to be drilled from inside the fuselage and then take it apart and install the collars (anyone who has assembled a Polish glider knows what these are.) Anyway, we finally solved the problem after installing new collars on both sides, a new pushrod and a new gear set.

So, a real lesson here. An accident, an inaccurately installed new wing fitting, the wrong pressure on the pushrods to try to get them adjusted so they would lock (just barely), the resulting rubbing on the spoiler boxes that was swing the pushrods. Aircraft was flown like that for 10 plus years. Finally a new aircraft mechanic said he would not sign it off because it didn't feel right (but he didn't know what the problem was.) A lot of hours spent three aircraft mechanics and myself to discover and then resolve each of the issues described above. Now the aircraft is finally correct. Had the new aircraft mechanic not exercised a high degree of caution to start the process in the first place, it was only a matter of time (maybe many years, maybe soon) where the pushrod on the new wing or the gear set on the old wing would have failed, that is if an accident wasn't first caused by the spoilers popping open.

As an aside, it appears that two things happened around the same time: the fatality when the gear set failed and a change in the company that manufactured the Junior. Whatever the cause, the newer gear sets appear to be made of a different material than the old ones. The old ones were a white plastic and the new ones are black. I would suggest anyone with a Junior look to see what they have, keep an eye on it and inspect the lateral rear sides of the pushrods where they enter the spoiler box. It is tricky to do because if you pull the spoiler up to peek in, the pushrod is pulled deeper into the wing but with a small mirror or an inspection camera it likely can be done. The alternative is to remove the pushrod which is a pain because it is really hard to remove and replace the attachment inside the wing blind at the root end.

On Wednesday, February 5, 2014 11:19:04 PM UTC-5, OneTango wrote:
This is a voluntary pop quiz. You're circling in a 30 degree left bank at 3000 AGL. You hear a thunk and the glider enters a spin. Your practiced spin recovery technique does not work in the usual amount of time. You look in the direction of the thunk and see that the left spoiler is full open, you confirm that the spoiler control handle is in the fully closed position. A quick look confirms that the right spoiler is full closed. What do you do next? Why did the left spoiler pop open. What just happened? To derive the full benefit of this exercise, you might respond to this thread with your answer before looking at any of the other replies. My hypothetical solution and explanation follows as the next comment.

Dive brake became uncontrollable. It does not matter why.
Apply opposite rudder and unload the wing by neutralizing the stick in pitch while also neutralizing aileron. Open other dive brake to balance assymetrical drag that is helping add yaw in the spin.
Upon recovery, determine if the glider is controllable with one brake open. It will be in any case I would expect.
Get to landable place with one brake out(less drag than 2).
Fly a bit tighter pattern to allow for what is effectively 1/2 brake.
Go to full brakes from high final to balance and allow "normal" landing.
UH

I've been thinking this would be a fun scenario to practice on a BFR, to give the student (who will surely appreciate it) practice at handling an emergency that really isn't an emergency.

When the student checks airbrakes on his/her downwind checklist (what downwind checklist? Ah, on the second flight then!), I grab the airbrakes and say "the airbrakes just stuck open." And shut up. Now the student's job is to quickly plan a full airbrake plus slip pattern. It's not a real emergency, because we can always close the airbrakes.

Has anyone tried this? UH, font of all wisdom on such things?

John Cochrane

On Thursday, February 6, 2014 11:01:32 AM UTC-5, wrote:
I've been thinking this would be a fun scenario to practice on a BFR, to give the student (who will surely appreciate it) practice at handling an emergency that really isn't an emergency. When the student checks airbrakes on his/her downwind checklist (what downwind checklist? Ah, on the second flight then!), I grab the airbrakes and say "the airbrakes just stuck open." And shut up. Now the student's job is to quickly plan a full airbrake plus slip pattern. It's not a real emergency, because we can always close the airbrakes. Has anyone tried this? UH, font of all wisdom on such things? John Cochrane

Stuck or frozen open dive brake condition is part of our pre solo training. It does happen in the Winter.
UH