DA62 road landing in Dallas, Texas

[howitser]

What if he left the alternators switched of? There was a 42 that happened to in ontario a number of years ago after coming out of the shop. The engines need power to run.

[Boatguy]

I think he'd have to have ignored a couple of ALT warnings on the panel, and watched the PFD/MFD go dark 30min before the engines died.

[howitser]

The pfd and mfd would be running on the g1000 backup. The engine batteries could be dead already. I dont have a manual but the prop not feathered might be no alternator or battery power avaliable to feather.

[tjmoody]

What if he left the alternators switched of? There was a 42 that happened to in ontario a number of years ago after coming out of the shop. The engines need power to run.

Interestingly, the alternator switches only disconnect the alternators from he main bus, not from the engine-related circuits. So even if the alternator switches are accidently left off during normal operation, the fuel pumps, ECU and ECU batteries still receive power if the alternator itself is working.

There is an interesting report in the UK AAIB publication from 7/2021 where a pilot departed with alternator switches off. The avionics eventually went dark but the engines kept running for the flight. The conclusion was that they would have kept running as long as they had fuel.

[tjmoody]

From the NTSB Preliminary Report posted today. Yikes! Not sure what to make of this.

"During the controller’s response, the pilot reported hearing a “pop” and observed the avionics
display screens lose power. A few seconds later, he observed both engines had lost power.
The pilot executed a forced landing onto an urban road, during which the airplane struck a
power line and road sign that resulted in substantial damage to the right wing.
An initial review of the downloaded engine and flight data indicated the airplane lost electrical
power to the avionics system and both engines nearly simultaneously, while at 2,000 ft msl
and about 5 miles west of RBD.
Initial examination of the airplane revealed incorrect wiring installation and blown inline fuses
for the backup electronic control unit (ECU) power system for both engines. The main battery
capacitance was tested and found to be low, near 70%. The airplane was retained for further
examination."

[Chris]

Yowza! So did the incorrect wiring of the ECU backup batterys cause the entire electrical system failure? I would guess so (Occam's razor and all), but it looks like the aircraft had made several flights since the last time it was in a shop. Or did the system try to switch over to backup ECU power when something else went wrong (e.g. alternators off, battery deeply drained, lowering the gear causing voltage/current drop) and then blew the fuses due to the wiring issue? Hopefully we get some more details later.

The Beechtalk thread on this referenced a procedure to test the ECU backup batteries on a DA42-TDI after they are re-installed by starting the engines and flipping switches and pulling fuses. On my DA42-NG, it looks like the 100hr inspection mentions checking the LH/RH ECU backup battery fuses and wiring, but I didn't find a procedure for testing the ECU batteries.

[VickersPilot]

Acknowledging it was a wiring fault but still perhaps an STC for higher capacity TrueBlue Lithium batteries with monitoring should be considered for aircraft. I would take this upgrade if made available (now on SF50, PC12 etc).

[RookieFlyer]

Yowza! So did the incorrect wiring of the ECU backup batterys cause the entire electrical system failure? I would guess so (Occam's razor and all), but it looks like the aircraft had made several flights since the last time it was in a shop. Or did the system try to switch over to backup ECU power when something else went wrong (e.g. alternators off, battery deeply drained, lowering the gear causing voltage/current drop) and then blew the fuses due to the wiring issue? Hopefully we get some more details later.

"Incorrect wiring installation" could perhaps mean cables were incorrectly routed or retained, resulting in insulation abrasion and eventually short circuit. The interesting part will be if this resulted from a standardized factory installation procedure or subsequent field maintenance or repair.

If the former, then 2022 is going to be an additionally annus horribilis for Diamond...

[CFIDave]

The NTSB report is in error describing "main battery capacitance" when they obviously meant "main battery capacity" of 70% -- a very different meaning. You'd think they'd be more knowledgeable about electronics.

Both engine alternators (and their voltage regulators) should have been generating close to 28 VDC for charging the main battery, keeping the ECU batteries fully charged, and supplying power to loads onboard the aircraft. DA62 automatic load balancing of the dual alternators will provide sufficient power even if one of the alternators were to fail; there's no need for load shedding due to single alternator failure.

Lowering the gear for landing could have generated a transient voltage drop, but one that should have easily been handled by the dual alternator voltage regulators -- even if the main battery was weak (i.e., holding only a 70% charge).

I'm guessing there must have been a short somewhere in the system that caused blown fuses and everything to shut down. But that's why the plane's electrical system has multiple busses, so that some power systems should have remained active.

[TimS]

Following posted on COPA:
---------------------------------------
Saw on FB, so must be true .
Loss of electric power and both engines stopped.

NTSB issue the preliminary report into the accident involving a Diamond DA62, N84LT, that occurred on October 15, 2022, near Dallas Executive Airport (RBD/KRBD), Dallas, Texas:

On October 15, 2022, about 1448 central daylight time, a Diamond Aircraft DA62, N84LT, was substantially damaged during a forced landing near Dallas Executive Airport (RBD), Dallas, Texas. The pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

A review of air traffic control (ATC) flight track data revealed the airplane departed Winston Field Airport (SNK), Snyder, Texas, about 1332 and climbed to a cruise altitude of 11,500 ft mean sea level (msl). The pilot descended to fly a visual approach to Runway 13 at RBD, lowered the landing gear, and contacted the tower controller for landing clearance.

During the controller’s response, the pilot reported hearing a “pop” and observed the avionics display screens lose power. A few seconds later, he observed both engines had lost power. The pilot executed a forced landing onto an urban road, during which the airplane struck a power line and road sign that resulted in substantial damage to the right wing.

An initial review of the downloaded engine and flight data indicated the airplane lost electrical power to the avionics system and both engines nearly simultaneously, while at 2,000 ft msl and about 5 miles west of RBD.

Initial examination of the airplane revealed incorrect wiring installation and blown inline fuses for the backup electronic control unit (ECU) power system for both engines. The main battery capacitance was tested and found to be low, near 70%. The airplane was retained for further examination.