NTSB Factual Report

On April 24, 2016, about 0945 central daylight time, a Probst Zenair 601XL single-engine amateur built airplane, C-GXLP, impacted a ground obstacle during a forced landing following a loss of engine power near Hempstead, Texas. The pilot was uninjured and the airplane sustained substantial wing damage during the impact. The airplane was registered to and was operated by the pilot as a 14 Code of Federal Regulations Part 91 personal flight. Day visual meteorological conditions (VMC) prevailed and a flight plan had not been filed. The airplane departed from the David Wayne Hooks Memorial Airport, near Houston, Texas, about 0925 and was destined for the Brenham Municipal Airport (11R), near Brenham, Texas.

According to the pilot's accident report, he reported the day before the accident, he calibrated the airplane's left tank fuel sensor and filled it full of fuel. He taxied and ran the airplane's engine about 20 to 30 minutes.

The pilot got a weather briefing and departed on the flight to 11R after he performed a preflight inspection of the airplane. During the before takeoff airplane check, the pilot checked the carburetor heat, secondary ignition system (second set of points and coil, second fuel pump), generator, oil pressure, and oil temperature.

The pilot, in part, subsequently stated:

The real question is if the generator was not charging I should have

seen it in the run up. I have an ammeter between the ground of the

battery so can verify it is charging-- normally I do this by switching the

"master" to "battery only" and verify amps (normal 3-4amps in normal

operation, 6 amps with landing light on) then turn it to "alternator &

battery" and verify that amps go to negative indicating battery is

charging.

9:24 takeoff:

I left landing light on(as usual), performed normal takeoff, right

departure to the west, climbed to 1800 [feet] until clear of mode C veil.

...

Around 9:38 Dynon switched to "battery power" So I knew there was an

issue with electrical and/or generator.

- did a cruising climb at about 75 knots

- I switched to alternate [secondary] coil/fuel pump and engine ran

worse, switched it back.

- I switched master switch to battery only then back to alternator and

battery (no effect).

- I pushed in the alternator circuit breaker (crowbar overvoltage

breaker) it was not out, no effect.

- I switched to other fuel tank (to right tank)

- Hunted for the private airport shown on charts north of Hempstead (I

later found out that it is no longer there)

- picked landing road or field next to road. Telephone poles and fence

were setback 20 feet from road.

- Transponder showed under-voltage warning

- engine had slight "hiccup" when running about 1 minute before it stopped.

- Main radio shutdown

- engine shutdown 9:40 (start switch did nothing.)

- pulled out portable radio set to 121.5 called that engine was out.

- Landed 9:45

The pilot indicated that the airplane's left wing hit a road sign about two feet inboard from its wingtip. The sign broke and the airplane turned into a ditch where the nose gear bent and the right wingtip sustained damage. He said, "If I had missed the road sign there would have been no damage."

According to the pilot's accident report, he reported that he held a private pilot certificate with a single engine land rating. He stated that he had accumulated 273 hours of total flight time and 157 hours of flight time in the same make and model as the accident airplane.

According to the pilot, the accident airplane, a Probst Zenair 601XL, was an all-metal, two-seat side-by-side airplane that was manufactured in 2008. The airplane was powered by a 100-horsepower, Corvair engine, which drove a Warp Drive propeller. The pilot used a conversion manual to convert the automotive engine to an airplane application.

The airplane's battery was an Odyssey PC680 battery. According to the pilot, a fully charged PC680 battery should be able to run the engine for three hours on the battery alone with all instruments on and with the landing light off. With landing light on, the total energy consumption goes to about seven to eight amps and the engine should be able to run on the battery only for two hours.

At 0955, the recorded weather at 11R was: Wind 160 degrees at 6 knots; visibility 10 statute miles; scattered clouds at 2,600 feet; broken clouds at 12,000 feet; temperature 22 degrees C; dew point 18 degrees C; altimeter setting of 29.93 inches of mercury.

The pilot recovered the airplane to his hangar. He subsequently traced wiring from the generator back to the battery. He said, "Very obviously one wire, the output of the regulator, was loose on the regulator." He indicated that the root cause was an electrical connection (1/4" spade) which was loose at the output of the generator's voltage regulator.

The pilot's safety recommendation stated:

1) During runup and periodically in flight verify the alternator/generator

is charging the system.

2) Install a light (and perhaps buzzer) that activates if charging system is

not working when RPM [greater than] 1700. Make this part of the runup

test in [conjunction] with the ammeter.

3) Use a trickle charger when airplane is in the hanger.

The author of the Corvair engine conversion manual was contacted and asked about the pilot's recommendation. The author, in part, indicated that the pilot's suggestion to use a trickle charger on an Odyssey battery goes against its manufacturer's instructions, as absorbed glass mat batteries are harmed by trickle chargers.

A representative from the battery manufacturer was contacted and asked for applicable directions to bring up the charge in Odyssey batteries installed in aircraft that may not be flown frequently. He, in part, indicated:

The following provides information pertinent to keeping an ODYSSEY

PC680 at a high state of charge throughout its service life for maximum

performance in experimental aircraft for engine starting and flight

operation.

1. For experimental aircraft operation, ODYSSEY batteries should not be

operated in aircraft when the batteries rested OCV (open circuit voltage)

is measured to be less than 12.50V or 75% SOC (state of charge) without

a full recharge before flight operation. ODYSSEY battery model PC680 in

this state of 75% SOC or less needs to be fully recharged with an

approved charge/maintainer of at least 6 amps rated as listed on the

ODYSSEY web site: http://www.odysseybattery.com/documents/ODYSSEY_approved_12V_chargers.pdf.

2. For aircraft storage times of one week or greater with known parasitic

drain on the battery even with the master disconnect switch in the OFF

position, a charger maintainer should be used continuously during

aircraft storage or a routine recharge schedule should be established

after [three] weeks of no flight activity. This recharge should be for a

time frame of 12 hours or more with an ODYSSEY approved

charger/maintainer. Any ODYSSEY PC680 battery with less than 12.50V

should be recharged using this same procedure.

3. Proper Charging procedures for the ODYSSEY battery can be obtained

on pages 15-17 in the ODYSSEY Technical Manual located at: http://www.odysseybattery.com/documents/US-ODY-TM-002_1214.pdf.

4. The PC680 battery has a 12 year design life. To obtain maximum

service life, it is recommended that the battery be kept at a high state of

charge (greater than 12.50V) throughout its life as stated in paragraphs

1-3 above. The use of a minimum 6 amp ODYSSEY approved

charge/maintainer is highly recommended to support this objective.

The pilot was advised of the engine conversion author's comments and the pilot indicated that this was an acceptable alternate recommendation:

Consult the battery manufacturer's applicable maintenance manuals which

specifies the correct charging method/device that matches the battery's specific

chemical process if the onboard system is not sufficient to charge the battery

during the flight and/or the airplane is inactive beyond a battery manufacturer's

recommend time period.

NTSB Probable Cause

A loose output connection from the generator voltage regulator, which resulted in a loss of power to the electronic ignition system, a total loss of engine power, and a subsequent forced landing, during which the airplane impacted a sign pole.