Grampa Pettibone

Gramps from Yesteryear: March-April 2001

Illustration by Ted Wilbur

Wild Winds

Editor’s note: Lt. Cmdr. Howard M. Tillison, USNR (Ret.), was officer in charge of Helicopter Antisubmarine Squadron (Light) (HSL) 30 Det A aboard USNS Harkness (T-AGS-32) in 1982 during the incident he describes here.

We were inbound in our HH-2D Seasprite to a promising landing zone (LZ) which was on a gently sloping coastal plane in the lee of a mountain range that rose from sea level to 3,000 feet within a couple of miles. Inbound to the LZ from the ship at 1,500 feet we had a 25-knot head wind, shown by comparing our airspeed and doppler ground speed indications. When I reached a good spot to begin a straight-in landing approach to the LZ, I started a normal descent and began reducing airspeed from 100 to 70 knots for a straight-in to final. We were attempting to land as closely as possible to a road which ran along the base of the mountains at the spot where they began their upward thrust from the coastal plain.

I suddenly noticed that things didn’t feel right. I looked down to see a 1,500-feet-per-minute rate of descent on the vertical speed indicator. My ground speed was also increasing and the mountains were getting bigger all the time. In the space of about a mile, the wind had shifted 180 degrees and was now dead on the tail. Instead of a straight-in to the LZ, I ended up button-hooking around. I landed uneventfully, facing back toward the ocean.

After analyzing the situation, my copilot and I realized that the easterly tradewinds were spilling over the ridge and forming a rotor in the lee of the mountains, which resulted in both a downdraft during our approach and a 180-degree wind shift at ground level. Luckily, we were lightly loaded, overpowered and had room to recover from a potentially hazardous situation by making a 180-degree turn prior to landing. If we had been heavy and failed to notice the wind shift prior to short final, we could just as easily have been in a settling-with-power, or power-settling (remember the tailwind) situation.

After that experience, we either had our ground party pop a smoke flare every time we approached an LZ in mountainous terrain, or we conducted a flyover at 1,500 feet and tossed out a roll of toilet paper to see what the winds were doing at ground level before commencing our approach.

Mountain flying is a different environment, even when the mountains are right there next to the friendly ocean and flat tropical beaches. Helo drivers should be aware of this potential problem before attempting to land on the lee side of a mountain and ending up with a tailwind instead of a head wind while trying to pull into a hover.

Gramps blamed the CH-53D Sea Stallion crew in “Lava Lament” (see Grampa Pettibone, Spring 2020) for failing to “determine the wind direction,” but it’s not always apparent when the wind has shifted 180 degrees as it did with me and probably did to the CH-53D pilots that day, in a relatively small space. If a Hornet is on final to a carrier and the winds go out of limits, the air boss or the landing signal officer can wave it off. It ain’t the same ball game when you’re in a helo trying to make it into an LZ without the benefit of having somebody on the ground to put up a windsock before you arrive.

Grampaw Pettibone says …

“Welcome advice for rotary wing pilots.”