MedFlightDoc
Active Member
I hate to have to write this, but I've been urged by many to put this out there for others to heed warning. It's tough to even talk or write about, but I hope others might learn something.
My aircraft is a 1991 RV-6, with an O-320 and fixed pitch sensenich prop, with about 1275 hours total time and ~780 SMOH. Pretty standard set up. I've owned for about a year, and flown regularly including two flights the day before this all started and multiple trips in and out of OSH during EAA a few weeks before.
Flight #1: Nighttime cruise home after picking up my daughter from the grandparents house. Easy flight from Milwaukee Timmerman to Middleton Morey (KMWC to C29). Heading west at 2500', checked in with Madison approach, talking to my daughter when the engine suddenly stumbles and starts to lose significant RPM. I immediately knee jerk thought I had run a tank dry and reach down to switch tanks. As I'm doing so, the engine picks back up and acts as if nothing had happened. So quickly in fact, that I didn't think that the switching of tanks had even kicked in yet. I had almost full tanks, so a dry tank was of course not the culprit. Rest of flight proceeds uneventfully with no issues. Leaving me perplexed. CHT, EGT, mags, RPM's, volts, amps are all normal when I get home and do an extensive check and run up.
Flight #2: The next day, go out to airport in afternoon to check things out again. All is normal. No issues with temps, pressures, run up or static RPM. Ambient temps were in mid 80's (about 83-85 or so). Take off seemed normal until about 250-400' or so when engine stumbles badly, lose significant RPM. I do something I probably should not have (no need to chastise me, I've done enough of it already in the last month) and make the impossible turn and get it back on the runway. I chose this option mainly because I was taking off on 09 at Morey-Middleton (C29) and the city of Middleton and Madison is to the east. I didn't want to go down in the city. At this point however, the engine is still turning over as I sit on the runway and taxi off. The FBO mechanics heard the engine cut, piled into a pick up truck and came racing down the taxiway expecting to find me off the end of the runway in the field to the west.
I do a runup, and all seems normal now. CHT, EGT, amps, volts, run up and even full static run up are all NORMAL. Taxi to the FBO. We pull the cowl and nothing seems amiss. Sump the gas, no debris or water. Start to think if vapor lock might be the culprit? This aircraft does not have baffling to the gascolator, but does have sleeved fuel lines from the gascolator to engine driven fuel pump to carb.
The mechanics look thru as much as they can over the next day and a half. The fuel vents are clear, gas is not an issue. Everything seems normal. Start it up again and on the ground all the temps and pressures are normal, normal run up, full static run RPM check on both tanks (per the mechanic) were all normal with one exception: there seemed to be low fuel pressure gauge readings of barely 1 psi with the engine driven fuel pump, but would increase to about 4 psi (normal) with the electric boost pump on. Running it up to full power with the electric boost pump on would also then see the fuel pressure gauge drop some but the engine was running normally the entire time with no stumble or dropped rpm. We were starting to think the engine driven fuel pump might be failing, but this scenario seemed unusual (their experience had been that they usually just fail, not a "soft" failure with things still running normally).
This then led to the question of what exactly was going on. We also only had one more day to fly, as the annual was set to expire. The mechanics didn't have it pinned down and it couldn't be reproduced on the ground as everything appeared to be working normally...
I make the decision to make one more test flight to see if we can narrow it down more and get more information as we don't really have enough go on.
Flight #3: Evening flight the day after Flight #2. Do it all over again, completely thorough pre-flight, check gas, check everything. Starts fine. Warm up, taxi, all checks are completely normal as is the run up and even a full static run up with the exception that the fuel pressure gauge on the engine driven fuel pump is low (~1) but comes up to ~4 with the electric boost pump. My plan is to stay directly over the airport.
Decide to take off, slightly down wind on Rwy 28 so as to take advantage of open farm fields if something happens...
Take off, fully expecting to put my glider training to use and...nothing happens. Normal take off and climb. Orbit over the airport and everything is normal. Boost pump off, then on. Full RPM speed run, banks, turns...nothing happens. All is normal.
Decide to call Madison approach and get a transponder code to climb up over the airport, which they give me and I then try to provoke it by doing a full power climb with boost pump OFF to see what happens. It climbs right up to 4000' msl without any hint of trouble or stumbling. The fuel pressure gauge is still doing the same thing however (~1 without boost pump, 4 with it on) so at this point I'm thinking that the engine driven boost pump is dying and will need to be replaced. Call up Madison approach again, sign off and descend.
Then, at probably the worst possible time, getting to pattern altitude or slightly below, about 2 miles from airport (I had drifted out and away while descending) then engine stumbles badly. Quick electric fuel pump on, get a brief surge, then stumbles again with loss of significant RPM. Cycle it again quickly while turning back in towards airport and get a brief surge and then the engine DIES. At this point my speed had started to decay while I was trying to troubleshoot at very low altitude, so I abandoned further efforts to relight in order to concentrate on flying.
Thought I was going to make it to the runway by turning a very quick and sharp base to final while sweating my altitude and best-glide speed in the turn. I was approaching the runway about half way down, at about a 45 degree angle from the runway heading, heavily banked to try and make it when I realized it wasn't going to happen. Rolled wings level while still about 20-30 degrees off the runway heading and tried to dissipate as much energy as I could in a full stall landing in the rough prairie grass and farm field adjacent to the runway. Came down pretty hard, probably stalled a few feet too high but was doing ok for the first 50 feet or so but the vegetation and/or the lip of the runway concrete caught the gear, wiped it out and as I transitioned to the concrete came up on the nose as I thought I was going to go over on it's back. Slid the last 50 feet or so up on the nose on the concrete. So I actually did make the runway...AND when the engine died, the prop had stopped horizontal, so not a scratch on the prop...
All switches off, canopy open, exit very quickly...
My aircraft is a 1991 RV-6, with an O-320 and fixed pitch sensenich prop, with about 1275 hours total time and ~780 SMOH. Pretty standard set up. I've owned for about a year, and flown regularly including two flights the day before this all started and multiple trips in and out of OSH during EAA a few weeks before.
Flight #1: Nighttime cruise home after picking up my daughter from the grandparents house. Easy flight from Milwaukee Timmerman to Middleton Morey (KMWC to C29). Heading west at 2500', checked in with Madison approach, talking to my daughter when the engine suddenly stumbles and starts to lose significant RPM. I immediately knee jerk thought I had run a tank dry and reach down to switch tanks. As I'm doing so, the engine picks back up and acts as if nothing had happened. So quickly in fact, that I didn't think that the switching of tanks had even kicked in yet. I had almost full tanks, so a dry tank was of course not the culprit. Rest of flight proceeds uneventfully with no issues. Leaving me perplexed. CHT, EGT, mags, RPM's, volts, amps are all normal when I get home and do an extensive check and run up.
Flight #2: The next day, go out to airport in afternoon to check things out again. All is normal. No issues with temps, pressures, run up or static RPM. Ambient temps were in mid 80's (about 83-85 or so). Take off seemed normal until about 250-400' or so when engine stumbles badly, lose significant RPM. I do something I probably should not have (no need to chastise me, I've done enough of it already in the last month) and make the impossible turn and get it back on the runway. I chose this option mainly because I was taking off on 09 at Morey-Middleton (C29) and the city of Middleton and Madison is to the east. I didn't want to go down in the city. At this point however, the engine is still turning over as I sit on the runway and taxi off. The FBO mechanics heard the engine cut, piled into a pick up truck and came racing down the taxiway expecting to find me off the end of the runway in the field to the west.
I do a runup, and all seems normal now. CHT, EGT, amps, volts, run up and even full static run up are all NORMAL. Taxi to the FBO. We pull the cowl and nothing seems amiss. Sump the gas, no debris or water. Start to think if vapor lock might be the culprit? This aircraft does not have baffling to the gascolator, but does have sleeved fuel lines from the gascolator to engine driven fuel pump to carb.
The mechanics look thru as much as they can over the next day and a half. The fuel vents are clear, gas is not an issue. Everything seems normal. Start it up again and on the ground all the temps and pressures are normal, normal run up, full static run RPM check on both tanks (per the mechanic) were all normal with one exception: there seemed to be low fuel pressure gauge readings of barely 1 psi with the engine driven fuel pump, but would increase to about 4 psi (normal) with the electric boost pump on. Running it up to full power with the electric boost pump on would also then see the fuel pressure gauge drop some but the engine was running normally the entire time with no stumble or dropped rpm. We were starting to think the engine driven fuel pump might be failing, but this scenario seemed unusual (their experience had been that they usually just fail, not a "soft" failure with things still running normally).
This then led to the question of what exactly was going on. We also only had one more day to fly, as the annual was set to expire. The mechanics didn't have it pinned down and it couldn't be reproduced on the ground as everything appeared to be working normally...
I make the decision to make one more test flight to see if we can narrow it down more and get more information as we don't really have enough go on.
Flight #3: Evening flight the day after Flight #2. Do it all over again, completely thorough pre-flight, check gas, check everything. Starts fine. Warm up, taxi, all checks are completely normal as is the run up and even a full static run up with the exception that the fuel pressure gauge on the engine driven fuel pump is low (~1) but comes up to ~4 with the electric boost pump. My plan is to stay directly over the airport.
Decide to take off, slightly down wind on Rwy 28 so as to take advantage of open farm fields if something happens...
Take off, fully expecting to put my glider training to use and...nothing happens. Normal take off and climb. Orbit over the airport and everything is normal. Boost pump off, then on. Full RPM speed run, banks, turns...nothing happens. All is normal.
Decide to call Madison approach and get a transponder code to climb up over the airport, which they give me and I then try to provoke it by doing a full power climb with boost pump OFF to see what happens. It climbs right up to 4000' msl without any hint of trouble or stumbling. The fuel pressure gauge is still doing the same thing however (~1 without boost pump, 4 with it on) so at this point I'm thinking that the engine driven boost pump is dying and will need to be replaced. Call up Madison approach again, sign off and descend.
Then, at probably the worst possible time, getting to pattern altitude or slightly below, about 2 miles from airport (I had drifted out and away while descending) then engine stumbles badly. Quick electric fuel pump on, get a brief surge, then stumbles again with loss of significant RPM. Cycle it again quickly while turning back in towards airport and get a brief surge and then the engine DIES. At this point my speed had started to decay while I was trying to troubleshoot at very low altitude, so I abandoned further efforts to relight in order to concentrate on flying.
Thought I was going to make it to the runway by turning a very quick and sharp base to final while sweating my altitude and best-glide speed in the turn. I was approaching the runway about half way down, at about a 45 degree angle from the runway heading, heavily banked to try and make it when I realized it wasn't going to happen. Rolled wings level while still about 20-30 degrees off the runway heading and tried to dissipate as much energy as I could in a full stall landing in the rough prairie grass and farm field adjacent to the runway. Came down pretty hard, probably stalled a few feet too high but was doing ok for the first 50 feet or so but the vegetation and/or the lip of the runway concrete caught the gear, wiped it out and as I transitioned to the concrete came up on the nose as I thought I was going to go over on it's back. Slid the last 50 feet or so up on the nose on the concrete. So I actually did make the runway...AND when the engine died, the prop had stopped horizontal, so not a scratch on the prop...
All switches off, canopy open, exit very quickly...