Single Point Control System Vulnerability

[Gary0747]

In doing my mental risk assesment of potential failures in our Mooney control systems I am thinking the eleviator controls are our biggest risk.   We had the AD on a failure of a aleron that I dont think resulted in an accident possibly because the other aleron still worked.  So the alerons might be considered to only have one or two points suseptable to single point complete failures.  The elevator appears to be a different higher risk system where a failure of a bearing, tube or pivot point could result in complete loss of the system. I think our Mooney systems of push pull tubes are much more reliable than the cable systems of the other brands.  I think the other brands cable systems probably get more and closer inspections but wonder that we might be needing closer inspection routines especially as our vintage birds get older?

I was wondering if others have found problems or have thoughts on this they could share?

[PTK]

We don't have an epidemic of loss of elevator control. But always proper maintenance is key.

[carusoam]

Preflight inspection and procedures usually give enough of an insight to know all bearings are working as well as every system is connected properly.

The looseness of bearings becomes evident over time.  lifting the tail gives a feel for wear.  Tugging on aerlerons and flaps and their control rods, same idea...

As you go through your check lists make sure you know why you are doing each step.  What you are looking for.

Review your check lists to see what has not been tested or improperly tested or can be tested better.

My favorite is reading how other people do their preflight activities and include their thoughts into my practices.

The biggest risk is the guy behind the yoke.  When he skips the pre-flight activity or misses things or doesn't recognize what he is seeing.

If there was only one thing to worry about, we would come up with a solution for the one thing.  

There are a lot of things.  Fortunately we have a solution for all of them.  Work those check lists. Use them.  Update them.

maintenance is key.  The flap control rod gussets were an AD around Y2K to strengthen the system.

There are going to be limits to the systems.  These are well documented in the POH.  If you exceed the limitations there are steps that can be taken according to the maintenance manual.  You can read what happens when people exceed the flap speed limit.

Asside from that...  If you want to do something to improve the safety of flight...

- avoid flying in thunderstorms.

- avoid flying in icing conditions.

- don't run out of gas.

- be prepared for an engine failure. Do not stall.  Have a solid plan to avoid the stall.

Thoughts of a PP,

-a-

[Mooneymite]

Should the elevator pushrod break, or jam, the elevator trim should still work well enough to effect a survivable landing.  I'm speculating.  I have no intention of trying it out unless I have to.  

[Gary0747]

Good point I think this using elevator trim to land actually happened a number of years ago and was reported in the MAPA Log. 

The AD was on the Aleron control rod gussets not the flaps. If I recall the incident that was the cause of the AD, it happened to a guy using is Mooney to fly pipelines but I dont think it caused a crash. 

Preflight is important but my concern is over the tubes, bearings and pivots that are not very accessable and may not get a good inspection even during most annuals. 

[Yetti]

Help with your next annual.  All the points get an inspection and some get lube....

[Yetti]

Having two people doing the looking is even better

[N601RX]

There is a single bolt that connects both ailerons to the control column, However it like all the other joints use locknuts making it extremely unlikely one will ever come off unless someone reuses them several times.

[Jerry 5TJ]

 

58 minutes ago, N601RX said:

There is a single bolt that connects both ailerons to the control column, However it like all the other joints use locknuts making it extremely unlikely one will ever come off ...

The most dangerous single point of failure is the nut on the pilot's seat.

 

[takair]

Trim is the backup to the elevator.  I know two people in brand P who have successfully landed after failure.  Even with an aileron failure we still have control with the rudder (assuming it is not jammed hard over).  Would not want to experience either, but I'm quite certain you would have limited control within reasonable wind conditions.

[takair]

As a follow up, from part 23.145:

"(e) By using normal flight and power controls, except as otherwise noted in paragraphs (e)(1) and (e)(2) of this section, it must be possible to establish a zero rate of descent at an attitude suitable for a controlled landing without exceeding the operational and structural limitations of the airplane, as follows:

(1) For single-engine and multiengine airplanes, without the use of the primary longitudinal control system."

This means that you must be able to land without elevator.  I am pretty sure our CAR 3 cert basis was similar.  You can practice this without too much risk by flying with power and trim. Elevator is always there if it does not go well.  Keep in mind, this is an emergency maneuver, so you just need to get on the ground without injury.  As a side note, in our Mooneys, we have the aileron/rudder interconnect, so some failure points may still provide some aileron authority through the rudder.  Here is another fun thing to try.  Hold ailerons in neutral and fly with rudder only.  May not be coordinated, but you will find you have some level of control.  That dihedral we have is like old three channel models and gives you some roll authority.  If I ever found myself in either situation, I think I would look for the longest, widest, into the wind runway and shoot for that.  

[N201MKTurbo]

Remember the DC10 in Souix City that landed with no controls at all. 

[carusoam]

CAR 3 rules essentially allows for one single point of failure...

the rudder can substitute for in-OP aerlerons...

Trim can be used in place of in-OP elevator...

Altitude can be used in place of in-OP engine...

 

practice and and training will be important to make this work.

 

in-OP control surfaces are pretty mild compared to jammed ones.

These are some of the nice things that come with a factory built aircraft.  Some of the benefits of them built the same way for decades.  A side benefit is MS where pilots can share their observations regarding failures and how to deal with them...

PP observations only, I'm not an aviation engineer or CFI or mechanic.

Best regards,

-a-

[HRM]

13 hours ago, Yetti said:

Help with your next annual.  All the points get an inspection and some get lube....

 

22 hours ago, carusoam said:

The biggest risk is the guy behind the yoke.  When he skips the pre-flight activity or misses things or doesn't recognize what he is seeing.

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