915Is ECU ISSUE

Jeff--Got with a factory rep from Montaer in Brazil.  He noted that their POH was inaccurate and the steps should be:

1-Key to the ACC position
2-Master On
3-Avionics On
4-PFD On
5-MFD On
6-Beacon On
7-Fully initialize the PFD & MFD
8-Alt Alternator- On
9-Lane A Mag-On (wait for light to go out)
10-Lane B Mag-On (wait for light to go out)
11-Check Engine Parms on Display
12-Primary & Alternate Fuel Pumps-On
13-Ignition-Start
14-Engine Items (Oil Pressure, RPM, Oil Temp, CHT, Fuel Pressure, Volts)-Green
15-Alt Altenator-Off

I thought the idea of the having the ignition in the ACC position was bizarre, but it seems to make a difference. He says that it provides some initial juice to the ECU. I also thing that having a low battery may have been a factor since the A&P's tried multiple starts. Don't know of any other airplanes that use the ACC prior to starting.  I had a Skylane for 24 years and never ran into an issue like this.

Thanks for the help and advice.  Hope this procedure makes a long-term difference.

Gene,

First of all, I flew a Skylane RG for about 20 years also, a great plane, but a much different animal.  I'm glad that its working, and here is some information that my help you understand what was going on. 

With the injected Rotax engines, the only things important in the starting procedure are that the lanes are energized, the lane lights have come on and then gone off, and main fuel pump is making pressure within spec. Most manufacturers only want minimum loads when starting, typically the PFD, the ECU lanes, and one fuel pump. I don't understand why your manufacturer would want the MFD, aux fuel pump, beacon, and Aux alternator on. The PFD is important to monitor the engine functions as you start the engine, but it would start without it. 

Here are a few important things to know about the Rotax Injected engines, along with some speculation about what might be going on. If you already know all of this, sorry in advance for being redundant. 

1. When the aircraft is being started, the ECU and fuel pumps need power from the battery.  Thats the "start power" that is often referred to.  Some aircraft have a start power switch that is closed for starting only, and other have it built into the ignition switch. It's important that Start Power is switched off after the engine starts so that the engine electrical system is then isolated. I don't know how Montaer handles the switching of start power, but it looks to be integrated into the keyed ignition switch. It may include a timing circuit to keep start power on until the engine starts, or it may be a simple mechanical function in the switch. Possibly the ACC position is important to initializing the start power sequence. If start power is removed too early in the start cycle, voltage will be dropped to the ECU and the lanes will go into fault. I have a hunch that this is where the problem was.     

2. Once the engine starts, the ECU is powered initially by Alternator B.  After you reach about 2500 RPM for a few seconds and Alternator A is verified, the Rotax Fuse box switches the alternators so that Alternator A powers the Engine functions, ECU, and fuel pumps. At the same time Alternator B is then connected to the airframe electrical loads, which also charges the battery. 

3. Once the engine is running, and start power is removed, the engine electrical system is fully isolated from the airframe electrical system including the grounds. In fact, at that point you can turn off the master switch and the engine will continue to run.  It's designed this way so that the engine electrical system is protected and independent.

4. If there is a failure of Alternator A, the ECU takes back Alternator B to keep the engine running, and your battery is then powering the airframe loads and not being charged. If Alternator B then fails the engine will stop. You then have the option of using the Emergency Power Switch to connect the battery to the engine, and then restarting. This is why Rotax requires a specific battery size - it's part of the engine electrical power backup system.  

Very interesting and informative.  May ask the guys in Brazil why the want to put such a load on the system.

Hi all

Note to Jeff, completely agree with your comment on the start with one pump.  The problem is the OEM missed the small note on the start procedure from the Rotax operators manual.  I attach the note from both the 912iS and the 915iS for Gene.  It would be good to tell the guys in Brazil it seems.  

Cheers

RW

I have to say that I continue to be surprised by how many mistakes SLSA manufacturers have made, and continue to make with respect to these injected engines. For the first couple of years when the 912iS came out I could almost understand it because the concepts were new to aviation. But now after 10 years I’m getting less forgiving.

The problem with fuel the pressure sensor not referencing airbox pressure never seems to go away, and several manufactures have missed required bypass valves and other fuel system components that are required with these higher pressure fuel systems. I’m convinced that at least a portion of the fuel pump failures Rotax had early on with these engines were actually fuel system design problems by the aircraft manufacturers. And when it comes to the start power control, you see all kinds of wacky solutions that seem targeted at making the aircraft start sequence more like a conventional engine, when in fact a simple start power toggle switch is not only more reliable, it also prompts the owner to have an understanding of what it does.  

I guess we could point to similar mistakes in the certified aircraft world, but it’s hard to imagine those mistakes being repeated this often.  The ASTM certification process seems inadequate to solve these problems across the diverse SLSA  manufacturing community. To the outside observer, it appears every manufacturer starts from scratch and makes the same mistakes.