New fuel pump requires Prist below +5C

[cttime]

I’ve heard that the new D64-9028-11-01 will be the only ones available. Reading the O09 supplement I was quite shocked to read that they will require the use of PRIST Hi-flash below +5C. That seems very restrictive.

Has anyone heard more about this? Anyone have experience using Prist before?

[MackAttack]

Thanks for posting; news to me. I was told that Prist would not be required when I took delivery of my 62 earlier this year. I have used Prist in my Piper turbine for several years. If you need it, you request “positive” JetA from the FBO. It’s usually a wee bit more expensive (a few cents really) than “negative.” Many smaller FBOs only sell JetA that’s already premixed with Prist. Could be slightly more of an issue outside North America.

It’s not a big deal but it will be good to nail this down. Much of the year, that 5 degree limitation will be applicable to most people.

Thanks!

[cttime]

Unfortunately Jet A+ is not really a thing in Europe so it introduces a bit of a problem needing it at such warm temperatures. Apparently the stuff is really nasty (corrosive and a carcinogen).

Interestingly enough the DA42NG with Austro engines and the same new pump doesn't require it (maybe due to the TC being European?)

[chili4way]

The pragmatic answer is that this should be no big issue, perhaps a few cents more per gallon in the FBOs that offer both options. In much of the US, and especially at smaller airports, PRIST is premixed with Jet-A. Prist (fuel system icing inhibitor) prevents any water suspended in the fuel from freezing. It does not prevent Jet-A from jelling or freezing (which is only a concern at much colder temperatures).

Technically, requiring PRIST removes the risk that suspended water could freeze inside the fuel pump while it is not operating. Except when the fuel pump switch is on, only the electric fuel pumps associated with the active ECU operates. The one not running isn't pumping warmed fuel so that ice crystals could develop and somehow prevent proper pump operation should ECUs switch. This could also happen to either or both pumps in a cold overnight situation.

Why this is happening now, with the introduction of a new fuel pump, is puzzling. It could be because the new fuel pump design or materials are different and more susceptible to suspended ice crystals in Jet-A. It could also be due to new, increased certification standards without regard to a specific increased risk associated with the new fuel pump.

Thus far, the Prist requirement only applies to the DA40NG and DA62. If the DA42 (and Austria-built DA62s) are now being built with this new fuel pump, we'll have to see if the DA42 also gets the Prist requirement. If so, it's a difference in the fuel pump. If not, it points to a difference in certification requirements between Transport Canada (DA40NG and DA62) and EASA (DA42-VI).

Pragmatically -- a very small difference in fuel price (where there is an option).

[CFIDave]

Flying a P&W PT6A-powered single-engine turboprop instead of a DA62, I'm now forced to use JetA+ with Prist: Outside temps at FL340 are as low as -54degC in the winter.

But unfortunately this does limit where I can land and refuel, since multiple smaller airports (e.g., those with self-serve JetA, often used for fueling turbine-powered helicopters) may not offer Prist. It's too much hassle to carry around a supply of Prist and add it to the fuel. So I no longer visit some airports (with cheap JetA, but without Prist) that I formerly visited to refuel our DA62.

[chili4way]

...since multiple smaller airports (e.g., those with self-serve JetA, often used for fueling turbine-powered helicopters) may not offer Prist.

In my experience, particularly at smaller airports (in the USA), the fuel is pre-mixed with FSII/PRIST. It may be worth a call to the specific FBO (or your brand-specific contract fuel supplier) to confirm.

The terminology around Jet-A fuels and options can be confusing to new owners. JET-A, JET-A+, and JET-A1 mean different things, and the availability and pricing available on websites don't always accurately represent which product(s) are available.

What I've figured out (and am always willing to become better informed).

• JET-A and JET-A1 are different in the hydrocarbon formulation and have different freezing points. This is unrelated to FSII/PRIST.
• When JET-A and JET-A+ are listed, the FBO offers a choice of with (JET-A+) and without (JET-A) FSII/PRIST.
• When only JET-A is listed (i.e., other than 100LL), it likely means the fuel is premixed with FSII/PRIST.

When in doubt, call the FBO. (It is always a good idea to check on fuel availability and that the truck/pump is operating at smaller airports). You might otherwise fly by an attractive fuel price.

[neema]

Is the 5°C limitation an OAT limitation? Or fuel temp limitation?

I was impressed how much the fuel pumps heat up the fuel on a cold night. -18°C (ISA-1) temps outside and fuel temps were still a nice 16/17°. This was at least an hour into the flight, too.



Reminds me of the diesel fuel AFM supplement. Here's a blurb from it:

[Boatguy]

Is the 5°C limitation an OAT limitation? Or fuel temp limitation?

That's a good question. I read it as an OAT limitation. If the pump has a problem with colder fuel, it seems to me that would begin with an ambient temperature at engine start below +5˚C. There is so little fuel burned in startup/taxi/runup that I don't think it has much chance to warm up a cold soaked tank of fuel before takeoff.

Without looking at all the part numbers I also don't know if this same pump is used for the transfer from the Aux tanks. But fuel in the Aux tanks is not heated by the engine so transferring potentially -15˚C fuel into the wings is going to chill the wing tank fuel.

In practical terms I think it means always having PRIST in the fuel.

[Colin]

It is definitely not the same pumps as those that do the fuel transfer (one gallon per minute, if I recall correctly). The high pressure fuel pumps increase the fuel temperature by putting it under very high pressure. The engine only sips a little, and all the rest gets dumped back into the fuel tank, heating the rest.

I can't remember where the fuel temperature probe is. If you are transferring aux tank fuel into the main tank you are doing it at a controlled rate (and could always switch it off for a bit). I flip that on then I am at 12 gallons in the main tank. If I saw the temperature dropping I would probably stop the transfer and wait a little bit for the main tank temperature to rise.

[Boatguy]

It is definitely not the same pumps as those that do the fuel transfer (one gallon per minute, if I recall correctly). The high pressure fuel pumps increase the fuel temperature by putting it under very high pressure. The engine only sips a little, and all the rest gets dumped back into the fuel tank, heating the rest.

I can't remember where the fuel temperature probe is. If you are transferring aux tank fuel into the main tank you are doing it at a controlled rate (and could always switch it off for a bit). I flip that on then I am at 12 gallons in the main tank. If I saw the temperature dropping I would probably stop the transfer and wait a little bit for the main tank temperature to rise.

The change which necessitates PRIST is to the dual electric pumps, not the engine driven high pressure pump (aka HPP).

The part number for the pump which transfers from the aux tank to the wing tank is not the same as the dual electric pumps which transfer from the wing tank to the engine.

As I read SB62-048, it says the "time of compliance" is at the owner's discretion. I interpret that to mean I should keep using the original pumps which don't require PRIST, but if/when one of those four pumps has to be replaced, then PRIST will be required. Unclear is whether making the change to all four pumps during the warranty period would be covered by warranty.