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NTSB Final Report, RV-4, N173CW, 6/9/2020

RV8JD

Well Known Member
Link to NTSB Final Report --> https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/101422/pdf

Link to Docket --> https://data.ntsb.gov/Docket?ProjectID=101422

Excerpt:

Location: Safford, Arizona
Accident Number: WPR20LA176
Date & Time: June 9, 2020, 08:46 Local
Registration: N173CW
Aircraft: Vans RV4
Aircraft Damage: Substantial
Defining Event: Miscellaneous/other
Injuries: 1 Fatal
Flight Conducted Under: Part 91: General aviation - Personal


Analysis:

The pilot was performing a routine flight over mountainous desert terrain to a destination he had flown to multiple times before. Visual meteorological conditions prevailed, with light winds and no turbulence.

ADS-B flight track information indicated that the airplane entered a nominal descent profile toward the destination airport; however, about 1 mile from the end of the presumed landing runway, the airplane began a rapid descent into rising terrain. After colliding with the ground, the airplane continued uphill 300 ft until coming to rest about 1/2 mile short and 40 ft below the approach end of the runway. The considerable distance travelled uphill after striking terrain indicated a relatively flat impact attitude and engine power at impact.

The rapid descent rate suggests that the pilot may have encountered pitch control difficulties; however, examination of the airframe did not reveal any evidence of primary flight control anomalies or a bird strike. The pitch trim system in the rear of the airplane was intact and functional; however, impact damage sustained to the front of the airplane precluded a complete determination of the pitch trim system state.

The airplane’s flaps were found fully extended, but flight track information indicated that the airplane did not slow to its flap deployment speed at any point during the approach. Damage to the flap electrical system prevented an accurate assessment of its operational status; therefore, an unintended deployment of the flaps could not be ruled out. However, under a runaway flap condition, the actuator motor would have deployed the flaps slowly, and flight testing revealed that any pitch-down forces caused by the flap deployment both with and without full nose- down trim would have been easily overcome by the pilot with the application of aft control stick forces. Further, at full extension, the flaps tended to act as air brakes. It is possible that he deployed the flaps intentionally to slow the airplane while struggling with a pitch anomaly.

During the examination, a foreign object (position light socket) that had previously been removed from the airplane was found in the lower underfloor bay of the aft seat, in an area that would have been occupied by the rear control column assembly. Although the forward control stick was fitted with a boot, the aft stick was not, leaving an open area into the control stick assembly. It is possible that either the socket or another unidentified object dropped into the open area and interfered with the free movement of the control stick, resulting in a pitch control jam and a rapid descent.

Probable Cause and Findings:

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

A loss of pitch control during the landing approach due to a jammed elevator control system.

++++++++++++++++++++++++++++++++++++++++++

Van's Aircraft conducted flight tests in support of the investigation which is discussed in some detail in the Final Report.

Also, on September 6, 2022, Vans Aircraft issued Service Letter 060, “Control Stick Opening Covers”. The letter addressed the possibility of foreign objects jamming flight control systems, and recommended that, when possible, all control stick openings where the stick passes through a floorboard or bulkhead should be covered by a stick boot.
 
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That's pretty awful and really sad.
While building mine I notice how close are some of the design clearances between control linkages and fixed structures. Something relatively small like a pen could potentially cause a jam.
I wonder if there is anything you can do in flight to possibly clear a control jam if it occurs?
RIP
 
...
I wonder if there is anything you can do in flight to possibly clear a control jam if it occurs?
RIP

Close to the ground, it will be hard. You'd have to have some amazing presence of mind to roll inverted and push if your stick was jammed from moving back.

I commend Van's for this SB - walking the line at KOSH I saw several RV-8s with no cover over the rear stick opening.

In addition, having just completed my second CI, it's important to account for any tools or mirrors or even screws that might have gotten under the floor during the inspection.
 
...walking the line at KOSH I saw several RV-8s with no cover over the rear stick opening.

Here's a simple one, just bent aluminum and a boot.
.
 

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That's pretty awful and really sad.
While building mine I notice how close are some of the design clearances between control linkages and fixed structures. Something relatively small like a pen could potentially cause a jam.
I wonder if there is anything you can do in flight to possibly clear a control jam if it occurs?
RIP

During my -7A build, I had kind of a "yikes" reaction to how close the aileron pushrod is to the rear spar passthrough hole:

...and how close the flap pushrod can get to the that fuselage passthrough that you have to carve into the bottom skin. You really have to pay attention and ensure there is zero opportunity for these controls to chafe or get caught up against other metal. I don't recall seeing any questionable passthrough for the elevator pushrod, but this thread gives me second thoughts. Might be something to double check during condition inspections.
 
My worst fears..

While building my -4, from the onset I planned a full covering of exposed control mechanisms. Too many things for a backseater to unkowingly jam up, as easy as dropping a phone/camera, sunglasses or whatever. Tandem aircraft are worse than side-by-side, as there is no way to see, or dislodge. In this particular case, the misfortune may have been to close to ground for any recovery, but the thought just gives me the chills. I have simple stick boots and full covers of both holes, as well as all the flap actuation and rudder cable side panels..only cost me about 2 lbs, max.
 
This post brings up an engineering question, that I do not know the answer to:
In a case like this - elevator will not go past a certain point - the pilot can gain some additional nose-up force by trimming for full nose down. Assuming the pilot can still hold the stick aft as far as it will go, how much more nose up degrees are there to be had?
 
Trim no bueno if jammed

If in fact the elevator linkage was jammed, the trim would not make a difference, and in fact would make it worse since the tab moves opposite of the required elevator input. In the case of this accident, I would bet the pilots thought process was in overdrive his hands were full just trying to understand what was going on.
 
It is true that if the elevator was jammed then the trim tab would not have any effect on the elevator, however it would act as a mini elevator in its own right, operated in the opposite direction to how it is normally used. The question is whether it is big enough to apply enough force to change the pitch of the flight.

We train for engine failures and how to recover from stalls, but my training did not cover what to do in case of a jammed control. Turns out there are stories of pilots who have recovered and survived these events and it appears that some aircraft flight manuals have emergency procedures for contol system jams and failures.

I think it would be worth putting such a section in my RV flight manual and rehearsing the procedure from time-time, same as practising stall recovery and forced landings. Of course prevention is important too, e.g. boots around control stick openings and vigilance during construction, periodic inspections and pre-flight checks.

A long time ago I survived an incident on a motorcycle when the throttle stuck open. Fortunately the designers provided a kill switch on the handle bar to deal with the event and I was lucky because it occurred unexpectedly.
 
Wow that would suck. If it was stuck in more or less neutral that would be one thing, but too much nose up or nose down and there's not much you could do about it other than ride it in.

Since we're telling stories, I have one from about 30 years ago; Had an acquaintance with a rag airplane. Think maybe it was a champ, but don't really remember, something with a fabric fuselage anyway.

He told me he had been doing a stall and couldn't get the elevator forward in the recovery. Really heaved on it with both hands and it popped loose.

After landing he found a screwdriver in the tailcone that had bound up in the elevator linkage and been punched through the skin from the inside during all his heaving and shoving.
 
This post brings up an engineering question, that I do not know the answer to:
In a case like this - elevator will not go past a certain point - the pilot can gain some additional nose-up force by trimming for full nose down. Assuming the pilot can still hold the stick aft as far as it will go, how much more nose up degrees are there to be had?

Well, given that the flaps apply a pitching moment that would tend to lower the nose, raising the flaps would be the first thing to try. Adding power might raise the nose as well... Maybe getting back up to an altitude where you have space and time to work the problem out might be preferable?

fixnflyguy said:
If in fact the elevator linkage was jammed, the trim would not make a difference, and in fact would make it worse since the tab moves opposite of the required elevator input.

Not quite... If your elevator is fixed, then the trim tab would work as a tiny little elevator of its own. So as he said, trimming for full nose *down* would move the trim tab up, and give you a tiny amount of "up elevator" in response. Would it be enough? I don't know. Alternatively, trying to trim for nose *up*, which might be more intuitive, could conceivably make it a little bit worse.
 
Jammed controls....

During the examination, a foreign object (position light socket) that had previously been removed from the airplane was found in the lower underfloor bay of the aft seat, in an area that would have been occupied by the rear control column assembly.

Years ago a good friend of mine was flying his 135 Super Cub and, on his turn from base to final, :eek::eek:, found his controls to be locked! As he was heading for a not good contact with terra firma, with both hands on the stick, pushed on the stick hard enough they freed up! Just in time to pull it out to an uneventful landing. VERY high pucker factor!

On the ground, he found the rear seatbelt latch had fallen in the small space in the floorboard and gotten caught between the stick and the aileron stop brace. The brace was bent out of the way by his superhuman efforts to free the stick in a moment of fast thinking. And, perhaps, some Devine intervention.

My rear seatbelts/harness in the Cub are holding two Cub bears in place and in SuzieQ are always buckled. Part of my preflight inspection.
 
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A few years ago we lost a local pilot moving a helicopter off a trailer - because a shotgun shell got wedged under a torque pedal. The helicopter was frequently used for hog hunting.

Be very careful when it comes to access to flight control hardware.
 
Also beware of other items that can jam your controls. I recently had a bit of a scare when on landing, I ran out of up elevator due to my ANR headset control. In flight and unbeknownst to me, it had fallen between my legs and was positioned between the control stick and wing spar in my 8.

Fortunately I had just enough control and made a bit of an ugly wheel landing. I didn't know why it was jammed until I was on the ground as it happened quickly and I didn't have time to trouble shoot.

You can bet I check that before landing now! I need to wrap that thing in Velcro and stick it to my harness somehow.
 
Elevator

There are also elevator control system failures. In some cases an improperly installed bolt falling out. Tom Cassutt had a bolt come out of the elevator pushrod connection on a cross country. No pitch trim system. After some experimentation he landed the airplane with no damage by shifting his weight for pitch control. Another more recent Cassutt had a failure of the elevator control system and landed without damage. This was at an air rce in the Middle East.
In the late 60's, Bill Stead, the originator of the Reno Air Races, died when a bolt came out of the elevator controls of his F1 racer on a test flight.
There were allegedly three cases with Beech 18's where the bolt came out of the elevator controls. All were landed safely with pitch trim and power changes.
This is actually quite easy with the Beech as the [pitch trim control is a large spoked wheel close to the left seat near the floor. One can stick a couple of fingers into the spokes and spin the wheel multiple rotations. Force involved is minimal. I have done takeoffs with just the pitch trim and have flown the airplane down to five feet or so on landing. That was enough to convince me that I could land the airplane that way.
 
I was in the back seat of a friends-8 over San Francisco Bay. Taking pictures of the skyline with a pocket camera. I dropped it. Guess where it went? That was a few seconds of panic. When we got back I built a cover for the rear stick in my own -8.
 
Control jams are bad news. I had one in 2005 at an aerobatic contest and nearly had to hit the silk. It became one of those "I learned about flying from that" articles:

https://www.rapp.org/archives/2005/06/i_learned_about_flying_from_that/

The odd part is that there's no way I could have seen the thing that jammed up the controls, because it was sealed up inside the wing.

Nevertheless I've found FOD in the tail of various planes I've been preparing to fly, from a Pitts S-2B to an Extra 300.

You might think planes with a sealed wall between the cockpit and the tailcone are immune, but my jam occurred in just such an airplane.

These days I spend more time preflighting aerobatic aircraft than actually flying them. It's impressive what you'll find. Keys, coins, pens, rings, watches, paperclips, wallets, cellphones, sunglass lenses, sequence cards. I even found a hearing aid one time. I hear (see what I did there?) those are expensive.

All that pocket change that isn't in the cushions of your sofa? Yeah, it's probably in the turtledeck of someone's taildragger.

--Ron
 
Velcro

When I bought my new to me RV4 a few years ago I was surprised that neither control columns had a boot over them to keep the fod out. One of the 1st things I had done was ask my girlfriend to make to nice boots out of some existing material that I had left over from the seats. Sewed in some Velcro and attached Velcro to the well. Works perfect and looks professional.

Another thing to keep in mind are that the rear seat belts are done up tight when flying solo. There have been more than 1 pilot over the years that loose seat belts in the back seat have caused fatality's.

Tim
 
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