Thursday, November 1, 2007
Helicopter Heroism: HOGE Sling Rescue at 18,040 Ft
IT WAS MIDDAY ON AUG. 8, 2005 when Lt. Col. Rashid Ullah Beg got the call to rescue a mountaineer from an elevation of 20,670 ft (6,300 m) on Nanga Parbat.
The Pakistan army aviator at once made a few calculations and concluded it was impossible to hover his SA315B Lama at that altitude at the prevailing temperatures. He recommended the mountaineer be brought down to, say, 18,000 ft, where a rescue attempt could be made. He heard nothing more and assumed his advice had been heeded.
That was until late that evening, when his corps commander told him he must undertake the mission. (The climber, Tomaz Humar of Slovenia, was a world-renowned mountaineer, and notorious for making solitary ascents by the most difficult and dangerous routes.) From that point, Beg considered it a military mission. "We had to attempt to accomplish it," he said, "even at the cost us of grave danger to our lives."
Beg contacted the famous Pakistani mountaineer Nazir Sabir, who had arranged Humar’s expedition. He painted a bleak picture. Humar was on the Rupal Face, a near-vertical wall more than 14,760 ft high. No one could climb to rescue him, Sabir said, and for him to attempt a descent would be suicidal.
The weather forecast for the next two days was favorable. After that, it would worsen for several days. Humar might not last that long.
Beg quickly ruled out a hoist operation for weight, center-of-gravity and power considerations. The density altitude would be nearly 23,000 ft. Hovering, even in ground effect, was impossible with his aircraft’s weight, he thought, let alone hovering out of ground effect (HOGE) and picking up a 150-lb (70-kg) man. The only hope was a sling rescue, he concluded.
The Lama was the right helicopter for the mission; it still holds the absolute altitude record of almost 42,000 ft. But Jean Boulet had stripped his Lama to an empty weight of 1,870 lb for the record flight. Beg’s Lama weighed more than 2,640 lb.
Beg drafted a plan that, he said later, "had very bleak chances of success, but was the only thing we could do." They would fly the mission with two Lamas and one Mi-17 in a support role. Beg and Maj. Khalid Amir Rana would fly one Lama from Qasim army aviation base in Rawalpindi to Astore, a village about 15 nm northeast of the climber’s base camp. Lt. Col. Ubaid ur Rehman and Maj. Mueen ud Din would fly the Lama from Skardu (along with the Mi-17 crew) at Astore.
From there, the three helicopters would fly to the base camp at 11,150 ft, where they would strip the Lamas of excess weight and rig the sling rope below the helicopter.
At 1415, they got word that the clouds had lifted and the Rupal Face was partially visible. Within 45 min, they landed at the base camp.
A day earlier, an Alouette from the private company Askari Aviation had photographed Humar’s position on the Rupal Face.
"When we saw the position on a photo and correlated it with the ground," Beg said, "our worries magnified a thousand fold."
In addition to the sheer face, there was a mushroom of snow on an outcropping 100 ft above Humar’s position. The only foothold was where he was clinging to the mountain by a small rope and an ice screw. Fresh snowfall made that mushroom an avalanche waiting for a triggering action, such as the wash or noise from a helicopter’s rotor.
While the helicopter needed to be light enough for HOGE, it had to be heavy enough to descend almost 10,000 ft in 10 min to keep Humar from freezing to death on the sling. The crews stripped the Lamas to bare essentials to reduce the weight, then prepared the sling rope.
They took off at about 1630. At 17,400 ft, they encountered clouds. Climbing further, they were almost in whiteout conditions. They finally decided to call off the effort for the day.
The next day, they could depart as early in the morning as possible. The air then would be denser. But the heavier air creates the downward flow of katabatic wind, which could be a big disadvantage. As the sun shines over a slope, the reverse happens and anabatic winds start blowing up the slope. The disadvantage there is the rising temperature would loosen the snow and increase the risk of an avalanche. The crews decided 30 min to 1 hr after sunrise would give them the maximum advantage. They planned to be in position when the sun had been below Humar’s position for almost half an hour.
On Aug. 10, they reached the base camp at 0545. A layer of clouds still hid Humar, but the sun was shining below him. The Lamas took off, the crews expecting the anabatic wind to push the cloud layer up as they climbed.
Beg and Rana did a last hover check at 20,000 ft pressure altitude while Rehman and Din in the other Lama took the lead in searching for Humar. Beg’s helicopter was stable enough, but the power pedal went to the limit. The lead helicopter spotted Humar, then cleared out for Beg and Rana, who initiated the approach to a spot slightly off the point where Humar was. They kept the wind on their power pedal, since a headwind approach was impossible. They saw the area from a close angle and executed a go-around to come in again. Now they were committed.
They hovered again, stopping the helicopter with Humar at 9 o’clock, the power pedal fully in. Beg said it was becoming extremely hard to maintain heading as they were running out of tail-rotor authority. They began inching to the left. Beg said the collective pitch indicator was reading.98 (or 98 percent power being consumed), barely enough to pick up 150 lb.
As they inched in, the force of the anabatic wind grew. They stopped to keep the rotor tips from hitting the rock. The collective pitch indication had dropped to.95-.96, Beg said, and a bit of power pedal was still available. Beg saw through his sling mirror that Humar was trying to grab the sling rope by reaching out with his ice axe as far as he could, but it was too far.
At this point, Beg and Rana were taking quick turns, alternating with one on the controls and the other breathing oxygen to avoid hypoxia.
They didn’t want to wear their oxygen masks for fear of the facepiece fogging up. Beg would hand the control to Rana and go on oxygen for about a minute, then Rana would do the same.
Rana, on the left side, had a better view of the rock face, and would tell Beg to stop movement when the snow started to blow just below the rotor disc. The outside air temperature was -8C (18F).
Beg pulled back, then moved back in and stopped short of the rock to swing the rope toward Humar. It was high-risk maneuver, but it worked. Humar grabbed the rope and clipped himself on. Rana, who then had the controls, said he felt a load on the collective. Humar gave the pilots a thumbs-up. Beg asked Rana to pull up.
Humar’s weight should have equaled a collective pitch rise of.02-.03, but the pilots saw it rise almost twice as much. Now the helicopter was hovering with 100 percent power and still not lifting up.
"Sir it is not pulling out," Rana said.
Suddenly, the helicopter started to sink and vibrate. Beg thought they’d entered vortex ring state and soon they’d all be dead. Beg looked into the mirror and saw the sling rope in full tension.
"Oh God," he thought, "he probably has not been able to cut his rope."
When the aircraft sank again, Beg took the controls and moved the helicopter to the right to the rotor tips hitting the rock. He then felt "a pronounced jerk" and the helicopter felt light.
"Sir," Rana shouted, "I think he has dropped." That sent a cold wave down Beg’s spine, but just then he saw Humar swing to the right on the sling rope. He immediately moved the helicopter further right so Humar would not swing back and hit the rock face.
They were clear of the mountain, but Humar was swinging badly below. It took Beg awhile to stabilize him. He then asked Rehman in the other Lama to close in and see if Humar was all right. To Beg and Rana’s relief, Rehman said Humar was fine and waving to him.
Beg established the required rate of descent and airspeed, then turned over the controls to Rana. Beg felt drained; Rana looked like he felt.