DA62 makes emergency landing on Dallas street

[PaulS]

Per the AFM there would have been a number of lights lit up and low readings if flying with both ALT out. And if he was, he owns this. What's interesting is those ECU back up batteries also power the alternator field windings in the event of a main battery failure and not just the ECUs and respective fuel pump. My SWAG is the main battery went belly up in flight and tripped the main CB which caused the #1 & #2 alternators to scram and instead of the #1 and #2 ECU batteries coming to the rescue smoked due to "improper wiring" on both systems. You would think at least one engine would have stayed running with 5 separate yet interconnected on board power sources. Ahhh, technology only as strong as the weakest link... or wire.

Or the main battery was TU before start up, he got a jump, got it going and went on his merry way. Hopefully not, but who knows.

 

[mondtster]

Per the AFM there would have been a number of lights lit up and low readings if flying with both ALT out. And if he was, he owns this. What's interesting is those ECU back up batteries also power the alternator field windings in the event of a main battery failure and not just the ECUs and respective fuel pump. My SWAG is the main battery went belly up in flight and tripped the main CB which caused the #1 & #2 alternators to scram and instead of the #1 and #2 ECU batteries coming to the rescue smoked due to "improper wiring" on both systems. You would think at least one engine would have stayed running with 5 separate yet interconnected on board power sources. Ahhh, technology only as strong as the weakest link... or wire.

Yeah. Looking at the schematic on the DA62, the only way I see the alternators remaining offline is if the pilot left the alternator switches off. The alternator switches and the master switch provide the ground circuit for the alternator relay with the ECU bus providing the power, which the backup battery is supposed to be tied to so that the alternators stay online. While there might have been some maintenance errors made I suspect there were some things going on in the cabin that led to this mess, and as Paul mentioned, perhaps the plane got jumped with a battery pack that did some electrical damage too.

If these engines were mechanically injected this thread would have never gotten created.

 

[Bell206]

Or the main battery was TU before start up, he got a jump, got it going and went on his merry way. Hopefully not, but who knows.

THats the same question I asked earlier. One thing I tried to get people to understand years ago when electronic cockpits were becoming the thing like with EFIS was don't take off with a shieet battery. 75% cap on this DA 62 battery doesn't happen overnight unless it was hurt bad. Be interesting to see the docket on this one.

the only way I see the alternators remaining offline is if the pilot left the alternator switches off.

The description also states there are alternator control units with no apparent reset function. And if you look at the emergency procedures for dual alternator failure it states you only have 30 minutes flight time which implies the alternators on running on the ECU batteries. So if the ACU trips the alternator off regardless of switch position your only option is the ECU battery to keep the alternator field voltage online. If you could get access to the maintenance manual version we could see for sure.

 

[mondtster]

The description also states there are alternator control units with no apparent reset function. And if you look at the emergency procedures for dual alternator failure it states you only have 30 minutes flight time which implies the alternators on running on the ECU batteries. So if the ACU trips the alternator off regardless of switch position your only option is the ECU battery to keep the alternator field voltage online. If you could get access to the maintenance manual version we could see for sure.

Yes, you only get 30 minutes of run time to find an airport before the engines quit if you have the alternator(s) offline, unlike if this were a mechanically injected diesel or the typical piston aircraft engine. The ECU batteries are only there to run the engine (including the alternator), not all the avionics, so if the main ship battery went south the cabin should go dark before the engines quit. I wonder if this pilot somehow thought the engines would continue running indefinitely so they just continued to fly despite having obvious problems?

The more I think about it, the more I suspect that might have been a couple of problems going on that were sort of related and happened to result in this mess.

Here's the maintenance manual.
http://support.diamond-air.at/filea...nce_Manual/Basic_Manual/70225-r3-complete.pdf

 

[Bell206]

The more I think about it, the more I suspect that might have been a couple of problems going on that were sort of related and happened to result in this mess.

Definitely more than one problem. At a minimum there was the initial power loss problem then the separate ECU battery supply problem (blown fuses) which I do not believe are related at all. Thanks for the manual link. Film at 11.

 

[Bell206]

might have been a couple of problems going on

FYI: European schematics still haven’t gotten any better.

All SWAGs, but seeing how things are connected doesn’t offer too many options for this type failure IMO. For a single fault failure to take out all 5 power sources, it would almost need to be a direct short at the Relay Box Bus which would have caused a cascade failure back to the backup batteries. But that would be highly subjective to the fuse/breaker trip speeds given the number of circuit protection devices in that route. So doubtful.

What’s interesting is they use spade connectors at the back up batteries for all connections. Definitely not murphy proof especially since one is connecting 2 batteries in series right next to each other for each system. And if the #1 and #2 backup batts were misconnected (reverse polar) in a similar fashion the installer probably wouldn’t even know it as there is no outside indication when the battery fuses blow and the DA62 manual gives a very vague function check (below #1).

I say vague because the function check (below #2) listed in the DA40 bulletin to install these back up batteries is much more detailed and would have shown if there was an install issue or blown fuse.

Also, the AFM only prohibits flight into Night VFR and IFR with an “empty” battery. So if this guy jumped started the aircraft and flew Day VFR he was legal but set himself up for a possible failure especially if he had an “unknown” issue, i.e., “improper wiring” with the ECU back up batteries. Regardless, I think we’ll see in the NTSB docket what specifically transpired which probably was more than a single fault. Glad I don’t have to chase sparks on these things.

#1 DA62

#2 DA40

 

[mondtster]

All SWAGs, but seeing how things are connected doesn’t offer too many options for this type failure IMO. For a single fault failure to take out all 5 power sources, it would almost need to be a direct short at the Relay Box Bus which would have caused a cascade failure back to the backup batteries.

Yeah, the failure as described doesn’t make much sense. I suppose a reverse polarity situation with a jump box might have caused some trouble that potentially would lead to something like this or maybe the wrong voltage.

One thing that I wondered about with the standby batteries is if the batteries were wired in parallel rather than series, making a 12v standby battery instead of a 24v one. Since a lower voltage would require a higher current draw to get the same job done that might have triggered the fuses to blow. It’s a mistake I could see a mechanic who is weak on electrical theory making.

That doesn’t absolve the pilot though, I think they shoulder a larger part of the blame. They almost had to have taken off with known defects to get this far.

 

[Bell206]

It’s a mistake I could see a mechanic who is weak on electrical theory making.

True, but same with a pilot/owner as well. With the unusual number of time scheduled batteries on this aircraft, there are a number of online discussions of US owners changing out these batteries under Part 43 preventive maintenance. Will be interesting to read the next report.