LauraE51
Pre-takeoff checklist
Sunday, on a flight from Modesto <KMOD> to Watsonville <KWVI>, i had to declare an emergency and land in San Martin <E16>.
The flight is one i've taken many times before, and, as with all flights over 30 minutes, i was on flight following. Now, the flight involves passing over two mountain ranges: one between the great San Joaquin Valley, which takes about 15 minutes to cross, and a smaller one between the highway 101 corridor and the pacific coast. That relatively narrow valley runs from San Jose south to Paso Robles in the south and is home to a variety of airports. The northern section of the valley, the part i pass over, is quite busy traffic wise, with departing and landing planes from San Jose International and GA flights from the local airports, one which i pass over on my way to the coast.
The initial parts of the flight were normal, with me cruising at 5,500 with the mixture leaned. As i came into the Gilroy valley, i began descending to 3000 feet before passing over the other side of the valley into watsonville. Just before i got midway through the valley, ATC asked me to level off at 4000 because of traffic. Shortly after, the engine RPMs began gyrating down and up. It wasn't the roughness you get from carb ice; it sounded more like the feeling when you lean the mixture too far, causing the RPMs to drop. In this instance, the RPMs decreased by several hundred before recovering to near normal, followed by decrease and increase again. It felt like the engine was going to quit at some point.
Now, midway through, i know i did put the Lean Mixture knob all the way to rich, but to be honest, i can't say what the effect was. After about 15 seconds of this, i let ATC know i was declaring an emergency, and i turned towards San Martin, which was just two miles away and landed. On the descent down to the airport, with RPMs at the 1700 level, i experienced no fluctuations.
After landing, i performed several high RPM run-ups to see if i could repeat the problem. I couldn't. After opening the engine door to see if anything was loose and performing another run up, i took off and returned to Modesto. I experienced no problems on the way home.
So, this could have been a mixture problem that would have worked itself out once i returned to full mixture, or it could have been something else. I don't know.
I'd say i was quite happy that i was on flight following, since ATC could warn me about traffic and i could reach out to them if i had trouble. They quickly gave me their attention, asked for my intentions, and pointed out San Martin, which i'd already eyeballed. Clicking on San Martin in Foreflight gave me their CTAF frequency and i told ATC i was switching over to advise traffic of my approach. To my pleasure, anther pilot had announced my emergency to San Martin's traffic, as did i a few moments later.....When i landed, that, or another pilot, told me they'd told ATC of my successful landing.
An event like this reminds me that i'm proud to be a pilot.
oh, and i'll be talking to our mechanic today, too.
The flight is one i've taken many times before, and, as with all flights over 30 minutes, i was on flight following. Now, the flight involves passing over two mountain ranges: one between the great San Joaquin Valley, which takes about 15 minutes to cross, and a smaller one between the highway 101 corridor and the pacific coast. That relatively narrow valley runs from San Jose south to Paso Robles in the south and is home to a variety of airports. The northern section of the valley, the part i pass over, is quite busy traffic wise, with departing and landing planes from San Jose International and GA flights from the local airports, one which i pass over on my way to the coast.
The initial parts of the flight were normal, with me cruising at 5,500 with the mixture leaned. As i came into the Gilroy valley, i began descending to 3000 feet before passing over the other side of the valley into watsonville. Just before i got midway through the valley, ATC asked me to level off at 4000 because of traffic. Shortly after, the engine RPMs began gyrating down and up. It wasn't the roughness you get from carb ice; it sounded more like the feeling when you lean the mixture too far, causing the RPMs to drop. In this instance, the RPMs decreased by several hundred before recovering to near normal, followed by decrease and increase again. It felt like the engine was going to quit at some point.
Now, midway through, i know i did put the Lean Mixture knob all the way to rich, but to be honest, i can't say what the effect was. After about 15 seconds of this, i let ATC know i was declaring an emergency, and i turned towards San Martin, which was just two miles away and landed. On the descent down to the airport, with RPMs at the 1700 level, i experienced no fluctuations.
After landing, i performed several high RPM run-ups to see if i could repeat the problem. I couldn't. After opening the engine door to see if anything was loose and performing another run up, i took off and returned to Modesto. I experienced no problems on the way home.
So, this could have been a mixture problem that would have worked itself out once i returned to full mixture, or it could have been something else. I don't know.
I'd say i was quite happy that i was on flight following, since ATC could warn me about traffic and i could reach out to them if i had trouble. They quickly gave me their attention, asked for my intentions, and pointed out San Martin, which i'd already eyeballed. Clicking on San Martin in Foreflight gave me their CTAF frequency and i told ATC i was switching over to advise traffic of my approach. To my pleasure, anther pilot had announced my emergency to San Martin's traffic, as did i a few moments later.....When i landed, that, or another pilot, told me they'd told ATC of my successful landing.
An event like this reminds me that i'm proud to be a pilot.
oh, and i'll be talking to our mechanic today, too.
