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#1
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MAYDAY in the Everglades
Hello everyone.
The end of my story is this; We landed safely in the middle of the Florida Everglades and didn't get a single Alligator bite. Here's what happened; On Friday, April 29th, we took our Cessna 152 from Lantana, Florida to the center of the State for gas and start our trek south to Key West. The total journey is a little over 2 hours. Forty five minutes after filling with gas in Pahokee, we were just below Alligator Alley (highway 75). Our engine hiccupped. A few minutes later, it hiccupped again, this time losing a couple of hundred RPM. We were at 6,800 feet, strait and level flight running at 75% power (about 2350 RPM). The mixture had been leaned back about 30 minutes earlier, and none of the engine instruments had changed from the time we made our cruise altitude. As the hiccups got closer together engine power dropped off significantly, grabbing our total attention. My first move was pulling up on the yoke to maintain altitude. I trimmed to our plane's best glide of 60 kts When the sputtering became a constant rough drone, the engine still held some power, and we could see nothing but marsh. I though about the choice between ditching in green or brown muck, not sure where the biggest alligators live. There was absolutely no solid ground as far as the eye could see. Solemnly, I rolled the 'standby' frequency to 121.5 acknowledging the severity of our predicament. Acting on the premise that the engine could quit at any moment and our best option was behind us on highway I75, I started a very gentle 180 degree turn. Oil pressure was in the green. Oil temp was in the green. Mags were on BOTH. The fuel showed close to full (I had at least 18 gallons useable). My only immediate change was to push the mixture to full rich, which had no effect. When I touched the throttle to add power, the RPM dropped. Gently, I returned the throttle and the power evened out. The sky was clear, and when I got my pre-flight briefing, the temp was 26 and dew point 16. It was unseasonably cool and very dry for Florida. At altitude, I knew the air had almost no moisture, but on the way up, we did have a typical hazy layer. My next move was carb heat, even though there was absolutely no visible moisture. It did smooth out the roughness slightly, but did nothing for the power loss. The engine was dying, and the math was simple. Sink at 500 fpt, 6,800 feet gives me about 13 minutes and at 60 kts, I'd get about 15 statute miles. I knew I could make the highway without an engine. I've personally had experience looking for downed aircraft in the Florida swamp, and know how difficult it is to spot a small plane. We needed to let someone know our position and situation. We had the skill to find the closest airport but every moment was precious. ATC could save valuable minutes and that might make the difference. With this in mind, I hit the radio's flip-flop button and announced our tail number on the emergency frequency. The Controller was a true professional. He asked me a few questions and instructed me to "ident" before assigning a squawk code. The radio reception was not clear, which generated a stream of "say agains". This, of course added to the general stress of the situation. Efficiently, he ascertained our position and vectored me to the Dade-Collier airport, which is in the middle of nowhere. Ironically, so were we! The strip was 17 miles to our southwest, which is farther than a dead engine would take me. We had been heading due north to a safe landing point on I75 when ATC advised us to turn our backs on the hwy and return south. In my heart, we turned away from solid ground to face only swamp again. I decided to trust fate and the ATC controller as I asked the alligators to gift me the extra minutes of engine power needed to make the airport. Trimmed back to slow flight, we managed to barely maintain altitude. We arrived at the 10,500 foot runway with 3,200 feet of altitude and 120 kts of air speed. I figure I could have made 4 complete turns around the pattern and still land hot. I have never been so relieved in my entire life. On the ground, we taxied to an area near two other planes. Relieved and curious I did a runup and the engine gave a text book performance. Our cell phones didn't work so we called the FBO on the radio. We were invited into the small building nearby where there was a phone. There we learned that the other two planes had landed the day before with similar symptoms. I phoned my mechanic and relayed the story. He gave me some great advice and a definite suggestion about what caused the problem. We returned to the plane to follow my mechanics instructions. Another mechanic, who had come to pick up one of the other downed planes kindly offered to look at my engine. He pulled the cowl open, checked the cables on the throttle, carb heat and mixture. He sat in the 152 with me while I did a regular and then full-power run up. The engine showed great response to throttle, the mixture choked it and the carb heat performed as advertised. This qualified mechanic was planning to fly out in a plane that landed in the same condition as ours. They offered us a ride if we were not comfortable flying our 152. We had options. Now, we had to make a decision to take the ride or hop in our plane and head out. The logic was: someone at some point would fly our 152 out, and we would again need to fly this same plane at some point ourselves. If we waited, what would be different? A qualified mechanic not only said it was safe, but was flying out a plane in the same condition. We decided the problem had resolved itself. We would fly. After a lengthy check, we headed for the runway. I did a steep climb over the field, continued uphill after completing a long, slow circuit of the airport, and headed north with a 500 FPM climb. All the while, I knew I could glide back to the runway if needed. It was late to start our day in the Keys so we turned towards home. When We sighted I75, I knew I was home free. If there was trouble we were guaranteed a level spot to land. We made Lantana at full power with no sign of the earlier problem. I must say, I am impressed with the FAA system and the people who dedicate their careers to the safety of our skies. This system that trains and relies on the good judgment of the individual pilot also supports the decisions necessary in crisis. While part of the mandate of the FAA is to enforce the laws, a pilot's decisions are respected even when they are examined. I find great comfort in the FAA and the service it provides to general aviation. If our highways resembled our skies, perhaps the average driver would be less likely to knowingly break the law. Here's my question to this group. What caused the engine failure? More than one thought is welcome, but please explain your answer. I have one of two possibilities in my head, and invite any questions, advise, opinions, or wisdom. Warm regards from one very happy pilot. Marty |
#2
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Carb ice. Of course, I wasn't sitting there with you so its just an arm
chair opinion. You say the carb heat worked as advertised but did you turn it on? Fuel venting. I'm trying to remember how a 152's fuel is vented. Is it vented caps or a venting tube? It could have gotten a bit plugged by dead bugs moving around. If you havent' already, I would remove the caps and blow air into the tank to see if there is any restrictions. Great job of handling an uneasy situation with professionalism. -Robert, CFI |
#3
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I'll agree to the carb ice... and sometimes.. if heat applied to late.. it
does not work.. one can expect the engine to run rougher after initial application of carb heat.. while the engine swallows the ice and water... then a marked improvement... sometimes people get the rougher engine and immediately turn the carb heat lever back to off and not give it a chance.. BT "Robert M. Gary" wrote in message ups.com... Carb ice. Of course, I wasn't sitting there with you so its just an arm chair opinion. You say the carb heat worked as advertised but did you turn it on? Fuel venting. I'm trying to remember how a 152's fuel is vented. Is it vented caps or a venting tube? It could have gotten a bit plugged by dead bugs moving around. If you havent' already, I would remove the caps and blow air into the tank to see if there is any restrictions. Great job of handling an uneasy situation with professionalism. -Robert, CFI |
#4
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Thanks so far for the responses. To elaborate;
The late model C152 (mine's a 1982), has a fuel vent for the left wing and a vent cap for the right side. I can blow bubbles up the vent tube, and in fact a primary consideration during my event was wing vaccuum. My head went to the wings, but I realized fuel starvation was more likely from a clogged fuel filter, or pinched line. There's no pump, just gravity. Regarding carb ice - Immediately after pushing the mixture to full rich without result, I added carb heat. It did very little, but I left it in, which is almost against my religion as it simply fouls plugs in the Florida climate, and little else. My thoughts on this one are simple; I'm at altitude on a brisk clear day, with NO VISIBLE MOISTURE. There was some cloud cover above (I estimate 10,000 + altitude). The effect of carb icing is simple - a gradual decrease in power with engine roughness, which is exactly what I experienced. The problem was, I had no further power reduction when I added carb heat, which typically occurs as the ice turns to water and temporarily fouls ignition. I should have seen an increase in power as the water blew through the carb. Also, why did adding throttle cause an RPM drop? Is this consistent with carb iceing? Also keep in mind that my flight was stable for about 30 minutes when the hiccup started. I hadn't flown through a cloud and there was no turbulance. I'll wait for some further input before adding my conclusion and the subsequent decision to take the plane back into the sky. Marty |
#5
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i can't imagine you would drop in the stuff about 2 other planes
arriving with similar symptoms if the mechanic there to ferry one back out didn't have a theory that gave both of you enough confidence to fly. with those temperatures, izzit possible that you're dealing with ice in the tanks? dan |
#6
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Carb ice. As the others have said if it's applied too late carb heat may
not have any effect once the ice has accumulated in the venturi. Visible moisture is not necessary for carb ice, you only need adequate humidity and according to Lycoming temps between 20 and 90 degrees F. Continental engines can form carb ice at even higher temps due to the position of the carburetor and remember that warmer air can hold more moisture than cold air so when carb ice develops at high temperatures it can be more severe. A full rich mixture can create carb ice even easier because now the carburetor is vaporizing more fuel creating a greater temperature drop. Adding throttle (fuel) can also cause an increase in carb ice due to the additional drop in temperature caused by the additional vaporizing fuel. After you landed and taxied around at relatively low RPMS (low amount of fuel vaporizing, warmer carb temps) the problem disappeared. Beware of it re-occurring on take off when you pour huge amounts of fuel through that carburetor again at full rich mixture. The non-textbook experience you presumably had with carb ice could be attributed to the engine ingesting chunks of ice departing first the throttle plate, then later off the venturi itself. The fact that several other airplanes in the area had the same problems also leads me to lean towards carb ice. This is the second post in as many months that has indicated that carb ice requires visible moisture. Structural ice requires visible moisture. Carb ice can form in visible moisture but it is not at all necessary. Either there are a lot of instructors mis-informing students on this matter or the FAA needs to get out a new AC on carb ice. Maybe both. Marty you did a great job holding your composure, thinking things through, and making good decisions. I'm glad you made it to the airport. Jim |
#7
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I"m not sure I agree with you regarding carb ice. While it may not have
been your problem, I've had carb ice in the J-3 that resulted in more than just a drop in RPM, the engine was doing next to nothing. Each time I've gotten carb ice it has been with not visible moisture. I think the visible moisture thing is just an old wive's tale. There is no need for visible moisture to get carb ice. Does the C-152 have a fuel filter? In my Mooney I have a couple screens but no "filter" per say. I guess the difference is that the screens (in theory) are for larger stuff and not as likely to clog. |
#8
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Marty
Forty five minutes after filling with gas in Pahokee, we were just below Alligator Alley (highway 75). Our engine hiccupped. A few minutes later, it hiccupped again, this time losing a couple of hundred RPM. We were at 6,800 feet, strait and level flight running at 75% power (about 2350 RPM). The mixture had been leaned back about 30 minutes earlier, and none of the engine instruments had changed from the time we made our cruise altitude. As the hiccups got closer together engine power dropped off significantly, grabbing our total attention. My first move was pulling up on the yoke to maintain altitude. I trimmed to our plane's best glide of 60 kts Good! Exactly correct for step one on the "Power Loss in Flight" checklist. When the sputtering became a constant rough drone, the engine still held some power, and we could see nothing but marsh. I though about the choice between ditching in green or brown muck, not sure where the biggest alligators live. There was absolutely no solid ground as far as the eye could see. Solemnly, I rolled the 'standby' frequency to 121.5 acknowledging the severity of our predicament. Acting on the premise that the engine could quit at any moment and our best option was behind us on highway I75, I started a very gentle 180 degree turn. Oil pressure was in the green. Oil temp was in the green. Mags were on BOTH. The fuel showed close to full (I had at least 18 gallons useable). My only immediate change was to push the mixture to full rich, which had no effect. When I touched the throttle to add power, the RPM dropped. Gently, I returned the throttle and the power evened out. The sky was clear, and when I got my pre-flight briefing, the temp was 26 and dew point 16. It was unseasonably cool and very dry for Florida. At altitude, I knew the air had almost no moisture, but on the way up, we did have a typical hazy layer. My next move was carb heat, You got this far before you tried step two! even though there was absolutely no visible moisture. The "power loss in Flight" checklist for the 152 says nothing about visible moisture...just do what it says! You took way too long to try carb heat. From what I understand, there are two reasons for using carb heat in the 152: 1) the obvious one and, 2) It bypasses the air filter giving you an alternate air supply for the engine. Other than that, you did a good job. I also fly out of Lantana and may fly that same plane. See you there, Vaughn |
#9
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"Marty from Sunny Florida" wrote in message
... ... We were at 6,800 feet, strait (sic) and level flight running at 75% power (about 2350 RPM) ... Peculiar cruising altitude, BTW (the glades aren't above 3800 feet, are they?) ... when I got my pre-flight briefing, the temp was 26 and dew point 16. It was unseasonably cool and very dry for Florida. At altitude, I knew the air had almost no moisture, With temp 26, dew point 16, there's definitely moisture there. Cool that air down to 16, and you'll start to get condensation.) At 6800 feet the OAT would have been cooler and the spread less. ... My next move was carb heat, even though there was absolutely no visible moisture. NB: There is absolutely *no* requirement for 'visible moisture' for carb ice to occur. It did smooth out the roughness slightly, but did nothing for the power loss. ... As others have observed, this is entirely consistent with carb icing, and (if you didn't (you didn't actually say)) you should have left the carb heat on. The unusual cold (for Florida) and the couple of planes that had the same problem the day before would suggest this as well. It's lookin' like Florida doesn't get enough experience with carb icing. (I'm not criticising, just jealous.)) But good job!, and good story. |
#10
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"Marty from Sunny Florida" writes: [...] The sky was clear, and when I got my pre-flight briefing, the temp was 26 and dew point 16. It was unseasonably cool and very dry for Florida. [...] If these are in degrees Celsius, then there is ample moisture in the air. My next move was carb heat, even though there was absolutely no visible moisture. [...] You misunderstand the nature of carb icing. Visible moisture (rain? cloud? thick mist?) is not a prerequisite. - FChE |
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