Terror In The Mountains - military helicopter and turbulence - Brief Article

Approach, Dec, 2000 by Rob Smith

I was on my first WestPac as a helicopter second pilot (H2P) in an H-46 detachment. We had just arrived in the Arabian Gulf, and I was part of a one-helicopter-and-crew mini-detachment to Fujairah in the United Arab Emirates. The short, good-deal trip had been extended to eight days when our diligent crew chief discovered a fuel leak from the No. 1 engine, which meant changing a fuel-control unit just before we departed on the afternoon of the third day. The HAC finally solved the logistics puzzle to return the helicopter to an up status, and we were ready to depart on our journey back to our ship, an AOE.

We arrived at the airport before sunrise, preflighted and loaded the helicopter. I journeyed over to the base-operations trailer to file an ICAO flight plan and check the weather for our destination and route of flight. The sky was mostly clear, except for a line of clouds just over the ridge of the mountains bordering the town to the north. The base-ops folks filed the flight plan and told me the weather was clear for the entire route. The winds at the airport were blowing offshore at 12 knots. I returned to the aircraft and relayed this information during our mission brief.

We started the helicopter, embarked our two maintenance-team members and headed for the mountains. The Navy course rules from Fujairah to Jebel Ali, our destination, followed a highway through the mountains at 1,500 feet. I was at the controls when we picked up the highway and began to enter a wide valley with 2,500- to-3,500-foot peaks on either side of us. We hadn't encountered any gusts up to this point in the flight and had heard no warnings about turbulence during the airport weather brief. Nevertheless, in the middle of that valley at 1,500 feet, we ran into severe turbulence.

The helicopter violently pitched up, and my stomach rose to my throat as we lost 300 to 500 feet in seconds. The aircrewmen later told me that they saw the fully loaded cruise boxes in the cabin lift form the deck. Moment later, we were caught in an updraft, rocketing 300 to 500 feet in the other direction. The entire episode lasted 10 to 15 seconds, during which time my control inputs had very little effect, even with full throws of the cyclic forward and aft to counter the extreme pitch variations.

The wind finally released the helicopter, and the controls gradually regained responsiveness. I scanned the sky above for traffic and immediately initiated a climb out of the valley. I contacted ATC to let them know we were climbing to avoid any more turbulence. The controller cleared us to 4,500 feet MSL for the mountain transit. We descended once we were clear of the mountains on the other side.

The remainder of the flight was very quiet as we reflected on what had happened. I hadn't experienced uncontrolled flight until this incident, and I don't want to be at the mercy of the wind again. The H-46 NATOPS states that the often-used procedure of flying through the middle of a pass (which I was doing) to avoid mountain "invites disaster." It specifies, "The procedure for transiting a mountain pass shall be to fly close aboard that side of the pass or canyon which affords an upslope wind. This procedure not only provides additional lift but also provides a readily available means of exit in case of emergency."

Although the course rules through mountainous terrain may specify a lower altitude, you can request clearance for higher altitudes from ATC to avoid turbulence. On subsequent flights, I chose this option and not only avoided the bumpy air but enjoyed the cooler air temperatures at the higher altitude.

Fly through mountains with great care. Turbulence may not be in the forecast and can occur unexpectedly. If you can avoid flying through the mountain valleys, by all means take that option and avoid the windy slopes.

Lt. Smith flies with HC-11