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Engine-out due to no fuel pressure

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5 months 2 weeks ago #20140 by thomago
Engine-out due to no fuel pressure was created by thomago
Dear Fellow Pilots,

I’m a newbie to Rotax-Owner.com and require your advice regarding major fuel pressure problems. The serial number of my Pipistrel Virus SW 100 is “355 VSW 100” and the Rotax 912 ULS engine serial number is “6776233”.

Flying in Thailand, I had various low fuel pressure warnings during 2 flights and 1 flight with engine-out due to no fuel pressure:

1. Low fuel pressure warnings: Both flights had a similar profile. Descending from 11,500 feet at a rate of 1,000 feet/min. Low fuel pressure warnings came on and went off after about 1 minute at 7,500 and around 4,000 feet. Then no more warnings until I reached 2,000 feet with warnings coming on again. The fuel pressure warnings were between 0.14 bar and 0.03 bar. During the time of the fuel pressure warnings, the engine seemed to run with a slightly limited capacity but not rough. Due to high non-standard temperatures in Thailand, density altitude is around 2000 to 2,500 feet higher than pressure altitude.

2. Engine-out due to no fuel pressure: During a recent x-country flight, I was flying straight-and-level at 7,500 feet for about 20 minutes. Then the low fuel pressure alarm came on. After about 10 seconds – with the last fuel pressure reading at 0.03 bar – the engine stuttered and then quit. I immediately put the plane on best glide speed. Tried to restart without success. Whilst gliding, I entered the clouds and was in complete IMC. No ground reference whatsoever. Flew the plane based on instruments and tried to restart again. No success. Finally, after the 5th attempt to restart, the engine started. I was still in IMC, stabilized the plane at 6,500 feet, and turned on the Auto Pilot. For the lack of better alternatives, I decided to continue flying in IMC (I’m IFR-rated but not current). I made heading and altitude changes only via the AP. Landed safely.

During the incident, I was flying mainly VFR-on-top in mountainous area of 3,000 to 5,000 feet about 50 NM from the next airport. Just glad the engine restarted at an acceptable height.

Afterwards, I test-flew the Virus for 2 hours at an altitude of 2,000 to 3,000 feet. No problems whatsoever but I was rather apprehensive and it was no fun. The fuel pressure problems seem to materialize at medium to high altitudes.

My Virus still has the original fuel pump from 2010 (P/N: 892542. The previous owner, based on a service bulletin, bought the recommended new fuel pump but it showed false readings. He then reinstalled the original fuel pump and never had a problem (so did other pilots I know who had experienced the same problem).

Engine-out in IMC and mountainous area can be quite a sobering experience and I do not wish to repeat this. Until I can solve the fuel pressure problem, I decided not to fly the Virus again. Right now I feel unsafe flying my plane.

I’ve ordered the recommended fuel pump based on the Rotax Service Bulletin (P/N: 893115) and it will be installed during the next two weeks. As a back-up, there is now also an electric pump (Facet).

I’m still very interested about the potential causes for low fuel pressure warnings and, especially, regarding the engine-out due to no fuel pressure. Any advice – especially how to avoid these issues – would be very much appreciated.

Amongst my flying friends who are quite knowledgeable when it comes to technical issues, one possible explanation was “vapor lock”. I’m a non-technical person and rely on advice.

Many Happy Landings,

Gottfried Thoma (thomago)
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5 months 2 weeks ago #20141 by garrett
Replied by garrett on topic Engine-out due to no fuel pressure
Is the fuel tank venting properly?

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5 months 2 weeks ago #20142 by thomago
Replied by thomago on topic Engine-out due to no fuel pressure
Garrett, being a non-technical person, I simply don't know. Will pose this question to my very experienced aircraft mechanic (US national) -- which makes a huge difference compared to the local talent available.

Thanks for your suggestion. Appreciate it.

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5 months 2 weeks ago #20143 by garrett
Replied by garrett on topic Engine-out due to no fuel pressure
Is the fuel tank venting properly?

Make sure you can blow air from the tank vent all the way into or out of the tank. Also the latest issue of September EAA Sport Aviation magazine has an article by Brian Carpenter of Rainbow Aviation on a dissection/explanation of the latest model Rotax 912 fuel pump and it shows a final stage filter buried in the pump non serviceable (that may be clogging).
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5 months 2 weeks ago - 5 months 2 weeks ago #20144 by garrett
Replied by garrett on topic Engine-out due to no fuel pressure
EAA September 2018 Sport Magazine Rotax 912 fuel pump pages 110 thru 113.
Last edit: 5 months 2 weeks ago by garrett. Reason: reword
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5 months 2 weeks ago - 5 months 2 weeks ago #20145 by garrett
Replied by garrett on topic Engine-out due to no fuel pressure
Also check to see if there is a fuel return line with restrictor (that's not clogged) back to the tank. The return line helps with vapor lock issues.
Last edit: 5 months 2 weeks ago by garrett. Reason: reword
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5 months 2 weeks ago #20146 by Roger Lee
Replied by Roger Lee on topic Engine-out due to no fuel pressure
One other thing to consider is angle of bank and or decent. Depending on where the fuel pick up is inside the tank and with a decreased fuel level you can un-port the fuel away from the pick up tube and it will make the engine think it ran out of fuel. I have seen this several times.

Roger Lee
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Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell
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5 months 2 weeks ago #20149 by Bill Hertzel
Replied by Bill Hertzel on topic Engine-out due to no fuel pressure
Summarizing...
Thailand, High Temperatures, High Altitudes.
Failure occurs after a long climb/cruise and/or after a throttle reduction.
A Hot Engine compartment and a reduced fuel flow at Idle/Descent are present.
The condition resolves itself after the engine has cooled for a while in the glide.

Sounds like a classic Vapor lock situation.
Are you using Auto-Gas or Avgas 100LL?
Confirm that the fuel lines are insulated in Fire Sleeving and are not routed near/above the Exhaust/Muffler/Cylinder heat sources.

An auxiliary electric fuel pump located close to the fuel tanks or at least right at the point where the fuel lines enter the hot zone is recommended.
This pump will add pressure to the fuel lines and prevent the vapor bubble from forming or collapse the bubble if it has already formed.
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5 months 2 weeks ago #20150 by thomago
Replied by thomago on topic Engine-out due to no fuel pressure
Garrett, thanks for the info. I've read the article about the new fuel pump and it's good to know how it works. Also, quite reassuring to read that most previous problems seem to be resolved.

My fuel pump, which malfunctioned, is still the old one from 2010 (soon to be replaced with the new one).

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5 months 2 weeks ago #20151 by thomago
Replied by thomago on topic Engine-out due to no fuel pressure
Roger, thanks for your comment which I will keep in mind.

When I had engine-out at 7,500 feet, I was flying straight-and-level at 5,000 RPM for about 20 minutes with fuel reserves of about 2 hours (about 40 liters/10 gallons). The AP was on.

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5 months 2 weeks ago #20152 by thomago
Replied by thomago on topic Engine-out due to no fuel pressure
Bill, thanks for your comments. Appreciate it.

I checked an instrument picture which I took shortly before I had the engine-out at 7,500 feet. On my Dynon EFIS, OAT was 17 degrees C (~62 F) and the stated density altitude was 9,600 feet. EGT's, CHT's and fuel pressure were all in the green.

I'm using Auto-Gas 95. I confirm that the fuel lines are insulated in fire-sleeves and are not routed near/above the exhaust/muffler/cylinder heat sources.

As of now, vapor lock appears to be the most logical conclusion but I'm still baffled how this can happen at straight-and-level flight for 20 minutes at 7,500 feet PA (9,600 feet DA). I understand that the service ceiling for the Rotax 912 ULS is 15,000 feet.

As you've pointed-out, high non-standard temperatures might be a key issue leading to vapor lock. At 7,500 feet, the standard temperature should be 0 degrees C (32 degrees F) but my OAT was 17 degrees C (~62 F).

Glad that I now have a workable auxiliary electric fuel pump as back-up.

Since I will continue flying in Thailand with high non-standard temperatures, are there any other ways to prevent or minimize vapor lock?

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5 months 2 weeks ago - 5 months 2 weeks ago #20153 by garrett
Replied by garrett on topic Engine-out due to no fuel pressure
I used to have similar problems with the old style pump. When pressure started to drop I would put a few drops of engine oil in the top weep hole between the pump mounting flange and the pump diaphragm, this would always bring the fuel pressure back up. This meant that the shaft was sticking due to lack of lubrication and was pounding on the eccentric on the prop shaft. This in turn damaged the end of the shaft on my new style pump which was discovered during a gearbox inspection/cleaning after many hours of 100LL use. Ended up replacing the pump again the and eccentric. You should visually inspect the fuel pump eccentric after removing the old pump for eccentric damage.
Last edit: 5 months 2 weeks ago by garrett. Reason: spelling
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5 months 2 weeks ago - 5 months 2 weeks ago #20158 by Bill Hertzel
Replied by Bill Hertzel on topic Engine-out due to no fuel pressure

thomago wrote: ... I had the engine-out at 7,500 feet. On my Dynon EFIS, OAT was 17 degrees C (~62 F) ...I'm using Auto-Gas 95.... vapor lock appears to be the most logical conclusion but I'm still baffled how this can happen at straight-and-level flight for 20 minutes at 7,500 feet PA (9,600 feet DA)...As you've pointed-out, high non-standard temperatures might be a key issue leading to vapor lock. At 7,500 feet, the standard temperature should be 0 degrees C (32 degrees F) but my OAT was 17 degrees C (~62 F).
Glad that I now have a workable auxiliary electric fuel pump as a back-up...


The OAT is irrelevant, The Temp of the actual fuel is all that matters.
Pressure Altitude, Not DA is the determining factor concering boiling.
Fuel in the tanks and sitting in the hot sun for a few hours before the flight may very well be hot soaked to a temperature above the ramp temperature. It will take a while for 20 gallons to cool down in flight.

Common U.S. Summer Grade E-10 AutoGas has a Reid Vapor Pressure (RVP)of 10psi.
This translates to a boiling point of ~40°C at 7500ft.
E-0 (RVP-9) fuel will allow ~45°C.
Less expensive Auto Gas (Winter Blend, RVP-14) will boil at ~30°C @ 7500ft.

If you have a fuel return line and it does not return the fuel to the fuel tank itself, consider that it will warm up a little each pass around the circuit.

If the AUX pump adds 4psi to fuel lines, that will move the vapor point to ~60°C or allow flights above 20,000ft.

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Last edit: 5 months 2 weeks ago by Bill Hertzel.

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5 months 2 weeks ago - 5 months 2 weeks ago #20161 by bstrachan
Replied by bstrachan on topic Engine-out due to no fuel pressure
I had similar fuel pressure problems for years with a 912ULS in a StingSport, including an engine-out 5 seconds into the takeoff roll. It's endemic to low-wing Rotax powered airplanes and is (I believe) a result of locating the fuel manifold on top of the engine where it gets good and hot, leading to vapor lock. In my case the flow restrictor (actually a carburetor jet) in the fuel return line was plugged solid, with what I do not know. Anyway once I corrected that, I have had no more issues. If you think I'm making this up, check out this accident report. The pilot reported vapor lock right after t/o and attempted to return to the field with a crash as the outcome. www.kathrynsreport.com/2018/03/czech-spo...persport-n422ps.html
Last edit: 5 months 2 weeks ago by bstrachan. Reason: bad wording

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5 months 2 weeks ago #20164 by thomago
Replied by thomago on topic Engine-out due to no fuel pressure
Thanks for taking the time and posting your comments, Bill. Appreciate it since it allows me to learn and become a better and safer pilot.

My following information is in reply to your comment that " The OAT is irrelevant, The Temp of the actual fuel is all that matters. Pressure Altitude, Not DA is the determining factor concerning boiling.
Fuel in the tanks and sitting in the hot sun for a few hours before the flight may very well be hot soaked to a temperature above the ramp temperature. It will take a while for 20 gallons to cool down in flight.
Common U.S. Summer Grade E-10 AutoGas has a Reid Vapor Pressure (RVP) of 10 psi.
This translates to a boiling point of ~40°C at 7500ft.
E-0 (RVP-9) fuel will allow ~45°C.
Less expensive Auto Gas (Winter Blend, RVP-14) will boil at ~30°C @ 7500ft.
If you have a fuel return line and it does not return the fuel to the fuel tank itself, consider that it will warm up a little each pass around the circuit. "

Additional information:

1. Before take-off for the x-country flight, my plane was hangared and not sitting in the hot sun. The temperature in my hangar was an estimated 30 degrees C (86 degrees F). After receiving clearance for start-up, I took the plane out of the hangar and took-off within 10 minutes. The sky was about 80% overcast so little direct sun exposure.

2. My x-country flight was for an estimated 250 NM -- lasting for about 2.5 hours -- and I flew between 3,500 feet and 7,500 feet. The OAT was between 25 degrees C and 17 degrees C (77 degrees F and 62 degrees F).

3. I was flying for more than 2 hours -- and the last 20 minutes straight-and-level with AP on at 7,500 feet -- when the engine-out due to no fuel pressure occurred. I would assume that the fuel in the tanks by that time -- due to cool ambient temperature for more than 2 hours -- was "cooled-down" to about 20 degrees C (68 degrees F). For obvious reasons, the fuel circulating the engine and going to the carburetors must have been warmer/hotter but still within safe parameters.

Based on the above, I'm still baffled about the unexpected engine-out at 7,500 feet PA with OAT at 17 degrees C (62 degrees F).

Unless there was something fundamentally wrong with the fuel pump, can you think of any other reasons why I had this incidence (besides possible problems with the fuel return line)? Would value your opinion. Thanks.

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5 months 2 weeks ago #20165 by eswallie
Replied by eswallie on topic Engine-out due to no fuel pressure
I find this interesting. I fly here in Las Vegas at temps above 110 deg. F (even up to 115 - 118) using plain old Costco auto fuel (91 Octane) and I have never had a problem with vaporizing fuel. My fuel pressure runs about 4 # with engine fuel pump and 6 # with elect fuel pump. Low wing, fuel return to left tank. Rotax 912 ULS with carbs. What am I doing right?
Ernie
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5 months 2 weeks ago #20169 by Roger Lee
Replied by Roger Lee on topic Engine-out due to no fuel pressure
I live in Tucson, AZ with the temps around 110F to and have never had an issue. The one thing to remember here is not all aircraft air flow and fuel hose installation is the same. Some don't have fuel re-circulation lines. So any heat build up on fuel hose can make a difference. The key may be re-routing hoses, make sure they are all in fire sleeve, wrap the exhaust pipes, make sure you do have unobstructed cool air flow through the cowl.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell
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1 week 3 days ago #21788 by ellisr
Replied by ellisr on topic Engine-out due to no fuel pressure
Hi Gottfried

Off topic, but was wanting to contact you regarding aviation in Thailand. Is there an email I can reach on you?

Russ

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3 days 4 hours ago #21865 by thomago
Replied by thomago on topic Engine-out due to no fuel pressure
Hi Russ,

You're welcome to contact me. The e-mail address is: thomago@gmail.com.

Cheers, Gottfried

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2 days 1 hour ago #21881 by TahoeTim
Replied by TahoeTim on topic Engine-out due to no fuel pressure
Do you have a fuel return line on your aircraft? If so it is a plugged return line or a fuel tank venting issue. On my 75 year old Ercoupe, it will not pull the last 25% of the fuel from the tanks if the fuel caps are not sealed properly or a cap is on backwards pointing the vent toward the rear of the plane. It also acts up if I am above 8000 ft. Now that you have a backup electric pump, you might be OK. My back up electric pump will not overcome the venting situation. Watch it carefully when you get to the same fuel level in the tank. Dropping in altitude will allow fuel to start flowing again if it is a venting issue.

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