Strange thing in the Diamond Manual

[TMetzinger]

We just got a new DA40XLS on the line here, and I've spent the morning going over the manual changes (increased gross weight affects W&B and various speeds like Va), and the supplement for the GFC700 strikes me as odd.

In an "old" G1000/KAP140 (or non G1000) model, the avionics master stays off before starting. Once the engine is running, you then turn on the Avionics master, and that will start the G1000 MFD and also start the KAP140 self test. Turning on the avionics master occurs later in the flow in the "before taxi" section, after the alternator is on.

In the GFC700 supplement, it calls for turning on the avionics master and letting the GFC700 self test before engine start, but it doesn't say WHERE in the "Before start" sequence this happens and it doesn't say to turn the avionics master back off. There's no mod to the "before taxi" section, so it seems to me that since "before taxi" says to turn it on, it should have been turned off earlier.

If anyone has gone through Diamond XLS standardization training from Diamond (not your local CFI), I'd appreciate your input on the sequence of events.

I'm inclined to have my checklist do the autopilot self test in the "before taxi" section, since it happens automatically when the avionics master is turned on. But I'm wondering if there's a reason the test should be performed before engine start. It is not normally performed before start in the Cessnas with the GFC700.

"Back in the old days" we left the radio master off because we didn't want to subject that stuff to the electrical deviations associated with the start and the alternator coming on line. However, a fair amount of the G1000 system is directly on the essential bus off of the battery, so perhaps there is sufficient electrical protection to not worry about this anymore.

 

[KennyFlys]

It's been a while since I've been in a DA-40 and I've never flown anything beyond a simulator with the GFC-700. So, the only question I can think of is...

Is there a switch for a standby battery you use to initially test the standby battery then turn on only the standby battery?

If so, I'd think the Avionics Master would follow the engine start just as it does in the Cessna.

That's the case i the Skyhawk's Nav III. The only thing I can think of is Diamond is placing the standby battery on the Avionics Master then the Master comes up behind it before start.

My memory of the Diamond manuals is they weren't written in the best fashion and are far lacking in comparison to Cessna's manuals. The only way to really get a good understanding of the systems in the Diamond is to dig into the service manual which is also available on their web site.

 

[Teller1900]

They didn't mention anything about it in my DA-40 checkout. It's an XLS with the GFC700, and the first time the CFI had me turn on the avionics master was after startup. My only guess as to why they'd have you test it before start is in case it fails, you won't have to shut down immediately after starting the plane. But that's purely a guess based on nothing substinative.

 

[Richard]

I've seen that same thing in many Cessna manuals and certain Piper manuals.

 

[KennyFlys]

Tim, I didn't have any checklist with me when I responded earlier at home. Now, Matt's post is reminding me of the preflight portion where you are required to check the avionics fans for both the panel and the rear avionics bay.

If it has you turning on the Avionics Master during that portion of preflight, that would make sense. But, if this is during the "Before Start" checklist, it's most likely as I described earlier.

 

[TMetzinger]

Tim, I didn't have any checklist with me when I responded earlier at home. Now, Matt's post is reminding me of the preflight portion where you are required to check the avionics fans for both the panel and the rear avionics bay.

If it has you turning on the Avionics Master during that portion of preflight, that would make sense. But, if this is during the "Before Start" checklist, it's most likely as I described earlier.

That's for the Cessna..... where they do have that issue. Doesn't exist in the Diamond - there's no requirement to check fans. Diamonds don't have a standby battery either (at least not one that you test. There is an essential buss to shed load, and then there is emergency power for the standby instruments that is a battery connected to a safety-wired switch. Pull the switch and it's a mandatory remove/replace/rewire of the emergency battery.

I'm going to call Diamond in the new year and ask for their training manager.

 

[TMetzinger]

They didn't mention anything about it in my DA-40 checkout. It's an XLS with the GFC700, and the first time the CFI had me turn on the avionics master was after startup. My only guess as to why they'd have you test it before start is in case it fails, you won't have to shut down immediately after starting the plane. But that's purely a guess based on nothing substinative.

But at least it's the same airplane, and you guys did it the way that makes sense to me... so I feel a leetle better.

As mentioned earlier, Diamond manuals aren't that great.

 

[Teller1900]

But at least it's the same airplane, and you guys did it the way that makes sense to me... so I feel a leetle better.

As mentioned earlier, Diamond manuals aren't that great.

Ya, in the whole checkout he referenced the manual maybe twice, then said "here's how we were told to do it, and this is what works for us..." He never mentioned a thing about turning the avionics on any time before the engine was running, though (in fact he said if you have to, do so only very quickly to save Bat power), so .

FWIW, I've flown the XLS for about 10 hrs now and never had a problem leaving the avionics off until the after start, and that's what the CheckMate checklist they have in the plane says to do, too. I'll be interested to hear what Diamond tells you.

 

[Steve]

FWIW,

When the Aspen EFD first came out they recommended the unit be tied directly to the battery bus so that it would energize as soon as you closed the main master switch (not the avionics master, if you had one). The literature even mentioned the unit could tolerate the transients associated with engine start. I think they did that because it took so long for the original units to initialize. My shop connected it to the radio/avionics bus which has its own power switch because "that's the way we always do it". Aspen later revised their guidance and recommended the unit be powered thru its own separate switch off the battery bus. I had an extra "gyro" switch from when the old elec DG & AI were removed so I had them move the Aspen power supply over to it. I wanted to be able to isolate the unit without having to shut off the radios, if necessary. I think Aspen realized it might not have been such a good idea to have the unit "hot" whenever the main master was energized. Also, the 1.1 software upgrade reduced the initialization time dramatically. My standard technique is not turn on any electronics until after engine start and off before engine shut down.

 

[KennyFlys]

That's for the Cessna..... where they do have that issue. Doesn't exist in the Diamond - there's no requirement to check fans. Diamonds don't have a standby battery either (at least not one that you test. There is an essential buss to shed load, and then there is emergency power for the standby instruments that is a battery connected to a safety-wired switch. Pull the switch and it's a mandatory remove/replace/rewire of the emergency battery.

I'm going to call Diamond in the new year and ask for their training manager.

I put myself through the wringer in the Diamond books for the last hour trying to look for an answer for you. I haven't flown a Diamond in nearly a year so what I did know is out the window. I spoke with the other school on the field who has Diamonds. He was just as confused. There should be no reason for the Avionics Master to be turned on before starting. He was questioning if you had the correct documents provided.

Another part of the discussion was the DA-40 not having a standby battery at all. All that avionics and once the main aircraft battery dies, you lose everything but the analog standby instruments. So, no communications, electronic nav, nuttin'. That seems like an horrible design flaw to me. That alone makes the Cessna design far superior in my opinion.

 

[TMetzinger]

Have him check the GFC700 supplement (rev 2 - 6/8/2006) to the DA40 manual. The section in point is on page 11 of 17, normal procedures, in the BEFORE STARTING ENGINE SECTION.

Cessna and Diamond accomplish the same thing in two different ways. In the Cessna, you can have an electrical problem that renders the supply from the battery to the avionics unsafe, in which case you have the standby battery.

In the Diamond, you have the pilot-activated essential buss, which basically isolates EVERYTHING from the battery except essential avionics.

Both give you good battery life for the same basic equipment - the net result is the same. Then, in the Cessna you still have vacuum power for your standby instruments. In the Diamond, you hit the emergency switch and have dedicated electrical power for your standby instruments.

It would take a failed alternator with no noticing (and in a G1000, you get told right away) and/or a very stupid pilot to drain the main battery in the diamond instead of using the load shedding.