Phase One - Safety

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

TXFlyGuy

Well-Known Member
Joined
Apr 25, 2012
Messages
2,305
Location
Republic of Texas
Those propellers run as high as $21,500. That does not include the spinner…another $2,000.

And only one of the above aircraft was in Phase One flight test, with multiple inoperative and/or malfunctioning systems.

Two of the above were fatal.

D8108E4A-6189-4C3D-B31D-3BFBF289C45D.jpg

T-51 Crash Jim Auman 2.jpg
 
Last edited:

TXFlyGuy

Well-Known Member
Joined
Apr 25, 2012
Messages
2,305
Location
Republic of Texas
So...to wrap a ribbon around this and bring it to a close, here are the facts that matter:

Pilot In Command made a conscious decision to fly an airplane during Phase One flight testing with multiple known broken / malfunctioning / inoperative items and/or equipment installed, after being advised not to fly the airplane, and after the pilot-in-command stated he was just going to "taxi it".

The aircraft owner was 1200 miles away. Had no knowledge of the particular flight schedule, had no knowledge of planned flights on July 6, 2021.
In addition, the aircraft owner was never advised as to the multiple safety concerns that surrounded the aircraft.

You are free to draw your own conclusion.
84F4A2CB-464C-467E-BAF3-D3C6051CD36C.jpg
 

TXFlyGuy

Well-Known Member
Joined
Apr 25, 2012
Messages
2,305
Location
Republic of Texas
Thankfully, all of the pertinent evidence from July 6, 2021, has been preserved. On the digital FDR (Flight Data Recorder), and the CVR (Cockpit Voice Recorder).

In addition, we have full video from the Cockpit Video Recorder.
 

Saville

Well-Known Member
Joined
Apr 28, 2014
Messages
431
Location
Boston Ma
More of a lesson for me and less of a "conclusion":

No matter the distance, each flight should be physically signed off by the owner. No sign off - no flight. With today's communications, distance does not hinder that sort of communication.

Whether or not the owner should sign off on engine starts or taxi tests once the first flight has occurred is something for me to think about. Before the first flight - maybe so.

The sign off should include the purpose and objectives of the flight/mission. This could be initially supplied by the test pilot and discussed/agreed upon prior to sign off.

This protects both the test pilot and the owner.
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
8,589
Location
Saline Michigan
If the wiring to the G3X, the unit itself, or the sensors hooked to it short to ground and can draw enough amperage to pop that breaker that feeds your ECU, the good news is that you won't need the G3X in order to know your oil pressure or RPM anymore.
Why in the world would you connect anything else through circuit protection for the ECU? A problem in something unrelated to the ECU then puts you in a forced landing - Ahhhhh! ECU rank right up there in things that should have independent power, circuits, and circuit protection clear of anything else, maybe even provide independant power from two bus with diode isolation. If you must power multiple things together through one breaker or fuse, please do it with things that do not result in total avionics loss or engine shutdown.
 

Vigilant1

Well-Known Member
Joined
Jan 24, 2011
Messages
7,155
Location
US
Why in the world would you connect anything else through circuit protection for the ECU? A problem in something unrelated to the ECU then puts you in a forced landing - Ahhhhh!
Agreed, it is crazy. That was my (intended) point. If the G3X is on the same circuit as the ECU and overloads the circuit, the "good news" is that you won't need the G3X to know the oil pressure and RPM anymore (because the oil pressure will be zero and RPM will be whatever the breeze will provide).
 

FinnFlyer

Well-Known Member
Joined
Nov 19, 2019
Messages
70
Location
Bell, FL
Coming in on this thread late. The statement from the guy installing the O2 sensors that there no other option than powering them by the MoTec was nuts!
He added a relay, but not a breaker or fuse. Even adding a simple in-line fuse to the relay would have been a solution.
Did you inspect the power wiring to the O2 sensors? Near glowing hot exhaust area there's every chance they could have shorted to ground if not properly insulated.
Even a manufacturing defect in one of them could have caused the (intermittent) short from power to ground.
That would be consistent with the high current draw when take-off power was applied -- hot exhaust pipes.
Removing the O2 sensors because of the possible role they caused is a bit of a (understandable) knee-jerk reaction. Properly installed, with separate relay and fuse/breaker that will make it impossible to take down the ECU and other flight-critical systems, they can provide valuable information.

For a long time I debated with myself whether I should put my O2 sensor on the essential (always hot) bus or on the main bus. Ended up putting it on the essential bus protected by a 3 amp fuse. That should burn well before the fuseable link to the battery does.

Finn
 

TXFlyGuy

Well-Known Member
Joined
Apr 25, 2012
Messages
2,305
Location
Republic of Texas
The Bosch O2 sensors have self protection built in. If there is a short, or an over amperage problem, or any problem with an individual sensor, they shut down and take themselves offline.

Yes, there are other options. But this would have involved a complete new wiring harness design. At the time, we did not feel that to be necessary.

This plane crashed for one reason, and one reason only.

The FAA representative who saw the video told me this should never have happened.
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
8,589
Location
Saline Michigan
In the last few days, I have found out about the fairly high frequency of these sad accidents and participated in threads on the topic. Most concerning to many of us is the root cause is suspected, but not definitely proved and prevented. While I have criticized, I have been trying to contribute to an attitude of we should KNOW that the root cause of ECU shutoffs has been addressed and we should KNOW that ECU power is maintained in operation. I really am concerned that we are having needless accidents and want them to stop. Perhaps that attitude is present in the owners of these airplanes, but I find it important enough to emphasize.

Getting on to this accident with TXFlyGuy's bird. Things we know:
  • All buses were powered and stayed on throughout the accident flight;
  • Electrical system used to draw 18-24 amps;
  • HEGOs are supposed to draw somewhere around 1A nominal, as much as 2 amps during warm up - so 8 HEGO will draw as much as 16 amp
  • HEGOs are supposed to be internally current limiting;
  • Accident flight current draw was more than 50 amp, circuit appears to have ben saturated;
  • System should have been at 18-24 + 8-16 = 26 - 40 amps from history and HEGO specs;
  • Descrepancy of 10+ amps exists on power usage - what was drawing that extra 10+ amps?
  • MoTec M130 ECU
    • ECU circuit protected with 15amp circuit breaker, and this breaker is thought to have opened in flight, shutting off engine. Is a 15A breaker specified somewhere by MoTec for this ECU?;
    • I visited MoTec site and could not find a wiring guide for the M130. Several other models for 8 cylinder engines specified 12AWG ground wire, 30A relay for off-on control, and circuit protection of 20 amp;
    • 12 AWG wire will give 10C temp rise at 22 amp, so 20A fuse is very conservative protection for the 12 AWG and equivalent power circuits;
Hmm. If it were my butt in the seat, I would sure pursue the source of the extra 10+ amps of power draw AND the sizing of the circuit protection for the ECU. Charging system overload does not appear to have been an issue in the crash, but is still at issue.

Let's get into details on why I am so focused on these:

Ship's power should have been drawing no more than 40 amps and more likely no more than 32 amps on the takeoff roll, but was 50+:
  • We do not seem to know how much above 50, but we know it was way above what it should have been;
  • HEGO's warm up fast, they should have been out of warmup mode long before takeoff;
  • Source of the excess draw of 18+ amps is important to making the airplane useable and reliable:
    • Alternators running at capacity usually have shortened lives;
    • Systems running beyond charging capacity will draw down the battery and either brownout or shut down in flight.
  • Running the engine and not seeing the excess draw may seem to say "we solved it", but it can also mean that the path to excess draw is still present, requiring only the right circumstances to recur. A search for the cause and robust solution is in order.
If the M130 is specified as needing a 20 amp fuse (as its brethren use):
  • A 15 amp breaker is sized to "nuisance trip":
  • Nuisance trip is the term used to mean it will trip and disconnect the circuit during otherwise nominal operation;
  • Nuisance is hardly the right term for taking down the engine;
  • Further, if MoTec specifies a fuse and not a circuit breaker, the installed system may have shut downs even more often;
  • A circuit breaker for an essential system that has been tripped by overload should be, at minimum, be replaced with new product;
  • Determining MoTec's preferred circuit protection for the M130 and installing that sure seems to be important to me.
Going further, automatic cascading of redundant power supply to the ECU and a precious few other elements appears to be important to safe operations.

All of these comments may have applicability way beyond TXFlyGuy's airplane. There have been quite a few other T-51 accidents. Many seem to be follow power loss in flight with an otherwise healthy base engine, gearbox, and propellor. Many of these birds are using electrically dependant engines. A robust pursuit and elimination of power interruption is in order.

Bill
 

Saville

Well-Known Member
Joined
Apr 28, 2014
Messages
431
Location
Boston Ma
Any high speed taxi can become a flight for a variety of reasons.
Sure and there is a whole thread on the value of high speed taxi tests. So let's not talk about that here.

My point was wondering if a sign off for engine starts or taxi tests is a good idea/necessary.

If a high speed taxi test inadvertantly turns into a flight well the pilot can cut power and land within seconds.
One cannot cover all possible contingencies..was the inadvertent flight done on purpose or an accident? Well how much
do you trust your test pilot?

I'm not trying to cover all contingencies in an ironclad manner. I'm trying to work out, in my own mind, how much "procedure" is necessary and where the point of diminishing returns may be.
 

TXFlyGuy

Well-Known Member
Joined
Apr 25, 2012
Messages
2,305
Location
Republic of Texas
During taxi out on the crash flight, the amps were 36-38, +/-.
With application of takeoff power, the amps immediately spiked to 50+, and remained there until the CB tripped.

This amp gauge was in full view of the pilot at all times. He deliberately continued the takeoff, in the face of what was certain catastrophic events to unfold.
 
Last edited:

Vigilant1

Well-Known Member
Joined
Jan 24, 2011
Messages
7,155
Location
US
One cannot cover all possible contingencies..was the inadvertent flight done on purpose or an accident? Well how much
do you trust your test pilot?
In these instances, "trust" is a poor substitute for clear mutual expectations. Maybe in writing. That will benefit the test pilot as well as you. "Trust" is for unforseen circumstances (that are bound to occur).

If I were doing private test flights for people, there are some instances where I'd want every direction documented in writing. And if I suspected I'd be made the fall guy for an accident due to a poorly designed airplane, that's work I'd turn down.
 
Last edited:

Saville

Well-Known Member
Joined
Apr 28, 2014
Messages
431
Location
Boston Ma
In these instances, "trust" is a poor substitute for clear mutual expectations. Maybe in writing. That will benefit the test pilot as well as you. "Trust" is for unforseen circumstances (that are bound to occur).

If I were doing private test flights for people, there are some instances where I'd want every direction documented in writing. And if I suspected I'd be made the fall guy for an accident due to a poorly designed airplane, that's work I'd turn down.

The question was rhetorical, though I can see why it might not be viewed that way.

As I wrote above:

"I'm trying to work out, in my own mind, how much "procedure" is necessary and where the point of diminishing returns may be."
 

TXFlyGuy

Well-Known Member
Joined
Apr 25, 2012
Messages
2,305
Location
Republic of Texas
When do people buy flood insurance? After the house has flooded.

I will not make the same errors going forward, now that my house was under water.
 
Top