Never Again: Windsock warning

May 1, 2009

I’ve been flying more than 20 years, increasing my flying as my business has grown. I bought my first airplane, a Piper Turbo Saratoga, in 2006, got my instrument rating in it, and flew it 300 hours in one year for business and training.

I bought a Piper Malibu Mirage in January 2008, and that’s allowed my passengers and me to fly in pressurized comfort on longer missions. Our company expanded into San Francisco and Denver over the past few years, and I visit those offices almost monthly. Being able to fly myself is very convenient.

In July 2008, I was taking off just after noon from North Las Vegas Airport in the Malibu, which is equipped with two turbochargers to enhance performance at high altitudes. My Saratoga had better takeoff and climb performance, but the Malibu flies higher and faster at flight levels up to FL250.

On this day, my wife and I were the only two on board, and with about 100 gallons of fuel and one small overnight bag, we were under weight by about 280 pounds. It was a hot day already, with the temperature reported to be 105 degrees F, but on the tarmac it felt even hotter. In fact, it was stifling. The airport is 2,205 feet above sea level, and the density altitude on this day was closer to 6,000 feet. The winds were reported to be 170 at 12 knots, and I was given clearance for departure on Runway 25, which is 5,004 feet long. Most of the VFR traffic was taking off and landing on runways12R and 12L. (Runway12R is also 5,000 feet long.)

I did a quick calculation and saw that the crosswind was approximately 80 degrees off the runway heading. The wind speed was well within the capabilities of my aircraft. But it didn’t sink in that a 50-degree crosswind on Runway 12R would have been more advantageous. Once I had determined the winds and runway length for my assigned Runway 25 were adequate, I was pretty comfortable and didn’t think more about it.

While waiting for the tower to clear me for departure, I noticed the windsock change direction and it looked to be right down my runway—but the wrong way. In fact, the sock was nearly horizontal, which told me the wind was probably 15 knots or so, a pretty stiff tailwind. I quickly double-checked the runway length and confirmed it was 5,004 feet. I can generally accelerate to 60 knots in the first 1,000 feet, and 85 knots—the normal rotation speed—by 2,000 feet. So even though this was a hot day and it appeared that I had a significant tailwind, I saw no need to change my plan to take off on Runway 25. It was probably a momentary gust that swung the windsock, I reasoned, and it didn’t concern me enough to ask for a different runway.

In the next moment, the tower called and said my clearance would probably be delayed a few more minutes. I asked the tower for a VFR departure and said I could contact Las Vegas Approach in the air to pick up my IFR clearance. I had current charts laid out for the Las Vegas Class B airspace and felt sure that I could remain clear before contacting approach, so I took the VFR departure and rolled onto Runway 25.

As is my typical procedure, I entered the runway environment at the end and stepped on the brakes until the Malibu’s manifold pressure reached 32 inches and I felt and saw the turbochargers kick in. That took a while on this day, given the higher density altitude and the fact that I had to gradually enrich the mixture as I opened the throttle, but it still happened relatively quickly and I started the takeoff roll.

Heading down the runway, I noticed that I only accelerated to 50 knots or so in the first 1,000 feet, and then hit 70 knots by 2,000 feet—meaning that I had 3,000 feet of runway left. By the time I saw 2,000 feet remaining, I had accelerated to nearly 80 knots and began to rotate. The aircraft sluggishly left the ground and climbed very tentatively with about 1,000 feet of runway remaining. All the engine parameters were fine and I kept my hand firmly on the throttle, pushing it in as far as it would go. But I was still only getting about 39 inches of manifold pressure and the aircraft wouldn’t climb more than 200 feet a minute. I was barely 100 feet as I cleared the departure end of the runway, or so it seemed. With sweaty palms, I held about 95 knots. At about 300 feet agl, I pushed the nose forward slightly and increased the airspeed to 110 knots, and soon was able to maintain a 500-foot-per-minute rate of climb.

After about one minute, my wife asked me from the back seat if there had been something unusual about our takeoff since we didn’t seem to leave the ground for a long time and our climb angle was very shallow. At this time, we were out of trouble and I shared with her that this was the hairiest takeoff I had ever had.

While the temperature reported was 105 degrees F, it actually felt hotter and could have been closer to 110 degrees by the time I departed, since the ATIS was almost 40 minutes old. That difference, using the same altimeter setting, would increase the density altitude by about 300 feet.

Now, whenever I’m cleared onto the runway, I check the windsock visually and confirm the current winds with the tower before actually taxiing onto the runway. If I see the sock moving around depicting a variable wind direction, I consider the length of the runway and the density altitude before starting the takeoff. I plan to make this part of a more thorough checklist when operating at high density altitudes. A hot day, a relatively mid-altitude airport, and a tailwind can and do conspire to dramatically reduce takeoff performance.

Although I had considered the effects of high density altitude on performance, I had never simultaneously been challenged by a tailwind. It was a valuable lesson learned. I will also tell the tower when I see the wind direction change so suddenly, and I’ll either change runways or postpone my departure until the winds become more stable or consistent.

Rod McDermott, AOPA 1567203, is an instrument-rated private pilot who began flying in 1988. He has about 800 hours flying experience and owns and flies a 1996 Piper Malibu Mirage from Chino Airport in Southern California.