Originally published July - August 1993
Back on 2 May 93, Mike Pelletier and I were flying the mighty Piper Traumahawk, doing our best to use up the remaining money I had on account at Aronson's before I left town for Colorado. We had flown from Rosamond down to Calexico, practiced using flight following, cleverly avoided flying into Mexican airspace (which would probably happen if you flew the pattern on the south side of the field), and gotten upset at a twin that was flying B-52 patterns instead of light plane patterns. This last one was aggravated by the fact that she called "Turning Final" as we were turning base and we saw no one in front of us. About the time we were ready to turn final, she called "Short Final." I can see the runway and there is no one in front of me. Finally, my comfort zone was well penetrated and we pulled up and went around. About the time we got to the other end of the runway to turn crosswind, the twin showed up on what I would call "Short Final" (1/2 to 1/4 mile from the threshold). While this was all aggravating, it's not the point of this article. End of Diatribe #146.
The point of this article happened on the return trip. Pause for a second, put down this newsletter, and go get your Los Angeles Sectional. It's okay, I'll wait. .........Doh dee oh doh doh ........................ Oh, you're back! Turn to the south side and locate the coordinates N33/ 59' W116/ 28.5'. You should be just north of Palm Springs. This is where we were when the event happened.
On the way south, we had come through this area (Morongo Valley) at 7500 MSL (about 3500 AGL). We had experienced some turbulence, and decided to come back at 8500 MSL instead of 6500 MSL. On the return trip from Calexico, we were flying over the Salton Sea and up the valley toward Palm Springs (V137 airway). Our altitude was 8500 feet, and we had noticed a reasonably strong west wind; strong enough to require a noticeable crab angle. (The old "sliding sideways through the sky" feeling). We had also commented on the thick clouds sitting in the pass heading west from Palm Springs (going towards Banning). There were also some thinner clouds near the ground along our intended route of flight heading north, but the tops looked low enough that we would be able to go over them. Now we arrive at the point in question, following V386 airway. Mike was flying at the time, and had noticed he was slightly below our chosen altitude. Thinking this was a normal altitude fluctuation, he pulled up slightly to correct. Checking again a moment later, we were still low, so he pulled up a little more. That didn't seem to be taking care of the problem, so he added some throttle. This went on until we were down to 80 KIAS, full throttle, and still looking at about 200 fpm rate of descent.
I had been enjoying the scenery and doing some navigating during all of this, when Mike determined maybe it was time to see what I thought about all of this. He told me that we were still descending, and looking at the tachometer, it appeared that the engine was losing power. A quick look at the tachometer said that the RPM was down to about 2250, instead of 2500 like I would expect. My first reaction was to run through the standard downwind check to try to restore power. Pulling up to best climb speed at 70 KIAS, I checked: Master switch on, mags on BOTH, electric fuel pump on, carb heat on, mixture full rich, and switched tanks. All engine instruments indicated normal. No change, other than a slightly reduced rate of descent. In the back of my mind, I knew we would be okay, since we were 8000 feet above the Palm Springs Airport, and it was right behind us. After about 30 seconds, we tried turning off the carb heat, with no change.
Well, we had done all of the emergency procedures in the book for engine power loss, with no change. About this time we started thinking about other possible causes of our situation. Here's your chance to think along with us (You Are There, with your host Walter Cronkite). Review the conditions stated above and study the surrounding terrain on your chart. You will have 30 days to write down your response. Please remember to phrase it in the form of a question. .......(Hum Jeopardy! theme music to yourself until next time).
(Ed. Note: To be continued next month, same bat time, same bat newsletter)
(Editor's Note: When we left you hanging last month, Russ Erb and Mike Pelletier were facing certain doom in a Piper Tomahawk that had somehow lost interest in further aeronautical toil. We rejoin the impending crash already in progress....)
Did you get the correct question? Those of you with glider ratings probably did. The correct question is "What is SINK?" Look back over the conditions: Westerly winds blowing over peaks from 6598 to 11499 MSL toward us. We were caught in the part of the wave coming down off the mountains. After a quick check of the chart for restricted airspace, we turned to the right toward Yucca Valley, and shortly thereafter were climbing again.
So what can you learn from our experience? Several things. First of all, the RPM was down to 2200 because the airspeed was down to 70 KIAS. With a fixed pitch prop, the RPM will vary with airspeed for the same throttle setting. This was normal, and should not have been cause for alarm.
Second, know when to expect both lift AND sink. Flying around the Antelope Valley, we get used to thinking about lift. Fly over a dry lake bed, and suddenly your climbing. Your first thought is "Aha! Thermals" and you push over to maintain altitude. However, we're not as attuned to recognize sink because it doesn't happen as often. Normally we talk about mountain waves in terms of lift, but remember also that between the "lifts" is just as much "sink." And of course, the rotor underneath all of this near the ground is great for some nasty turbulence.
Another clue, although I can't find a meteorological explanation for it, is that low clouds always seem to be sitting on the Tehachapi Mountains whenever strong winds are blowing. Note in the case detailed above, low clouds were sitting on the mountains. If you see this, and of course any lenticular clouds, beware of mountain wave activity.
If you suspect that you are in some mountain wave induced sink, your best bet is to fly away from the mountains (assuming nothing prevents you from doing this), and eventually you will cross into the lifting part of the wave.
And for any emergency or odd happenings, remember your first diagnosis of the problem may not be the problem at all. Keep looking for alternatives until something solves the problem.
Contents of The Leading Edge and these web pages are the viewpoints of the authors. No claim is made and no liability is assumed, expressed or implied as to the technical accuracy or safety of the material presented. The viewpoints expressed are not necessarily those of Chapter 1000 or the Experimental Aircraft Association.
Revised -- 22 February 1997