All hell broke loose at 83,000 feet, just as a Soviet SAM site had the SR-71 Blackbird in its sights.
Summer 1984: the coldest part of the Cold War’s final years, when both sides were doing their best to keep tabs on each other. For the crew of SR-71 Blackbird No. 61-7974, flying at 83,000 feet off northern Norway, the sky was a dark purplish blue. The brighter stars were visible, and the earth far below gave no indication of their speed. After its final refueling, “974” climbed back to altitude, making a long 270-degree turn to remain west of Novaya Zemlya island. Pilot Joseph E. Matthews pushed the throttles forward, and the huge black dart accelerated toward its operational speed of Mach 3.2.
Seated in a separate cockpit behind Matthews, reconnaissance systems operator (RSO) Curt Osterheld checked his ASARS-1 imaging radar as the Kola Peninsula, now visible in the distance, grew larger. Atlantic Command was extremely interested in keeping track of the Soviet navy’s Typhoon-class submarines based at Murmansk. Meanwhile the radar-warning receiver let Osterheld know that the radars controlling Murmansk’s SA-5 missiles were “painting” his Blackbird.
At this point 974 was in international airspace and operating according to Peacetime Aerial Reconnaissance Program (PARPRO) rules of engagement, which required reconnaissance flights to be made along the same course at the same altitude each time. The speedy, high-flying Blackbird had been billed by some as impossible to intercept, but a SA-5—largest and most powerful of Soviet surface-to-air missiles—would have no trouble reaching it. Even a near miss would create a debris field large enough to endanger the SR-71. Fortunately, the Soviets used the Blackbird as a training opportunity for their operators rather than an actual target.
Osterheld monitored his equipment as they neared their closest point to Murmansk. Just as he was recording that a different Soviet radar had begun following them, all hell broke loose. “The airplane yawed to the right so far and so fast, it felt like it was going sideways!” said Osterheld. The SR-71’s right engine had just experienced an “intake unstart.”
During acceleration, the movable cones, or spikes, in the intakes of the Blackbird’s two Pratt & Whitney J58 engines retract into the inlet cowling. When the aircraft reaches maximum speed, with the spikes fully retracted, the shock wave spillage that causes turbulence over the outer nacelles and wings is minimized, while the shock wave off the spike itself is reflected between the spike body and the interior of the inlet, slowing the incoming air. As pressure builds inside the inlet, bleed tubes and bypass doors open to handle it and position the final shock wave so the inlet remains “started.”Air compressed by the interaction of inlet and shock wave is then diverted directly into the afterburner, where it is mixed with fuel and burned in what is essentially a ramjet, providing up to 70 percent of the aircraft’s thrust at speed.
But if internal pressures inside the J58 intake become too great, the shock wave suddenly blows out the front of the inlet. During an intake unstart, the computer controlling the spike records the lack of pressure and responds by moving the spike forward to the subsonic flight position. Airflow immediately stops, thrust drops and exhaust gas temperatures rise.
In the front cockpit, Matthews knew their only hope of avoiding disaster was to unstart the left engine, then attempt a manual midair restart of both. As thrust died in the left J58, it too unstarted. “It was like we hit a wall, the deceleration was so sharp and so fast,” Osterheld remembered.
Without power, the big Blackbird had the glide ratio of a brick. “We were going just about straight down,” he said. Below them were the icy waters of the Barents Sea. As 974 dropped like a stone, alarms went off at the Soviet air defense headquarters and at the NATO radar sites in Norway following the flight.
“Joe tried the auto-restart switch three times and got nothing,” Osterheld recalled.“We were close to punching out when he managed to get things re-lit manually.” Both men were crushed in their seats by the G-force of the pullout as they leveled off after falling to 18,000 feet in less than two minutes. They had avoided going nose-first into the sea, but now the question was whether they could get back home.
“There was no way we had the fuel to attempt to accelerate again, which meant we had to stay down low and subsonic,” he said. The SR-71 is most efficient at higher speeds and altitudes, since the airplane burns nearly the same amount of fuel to fly subsonic down low as it does to cruise in the upper stratosphere at hypersonic speed in terms of pounds burned per mile traveled. “We started calling for support as we headed south. Normally, when we would come off a Barents run, we would turn southwest and hit the tanker where we’d left them off the west coast of Norway, but with our fuel consumption what it was now, we were going to be short by a couple hundred miles if they couldn’t come to meet us. We thought of trying to put in at Bannock or even Bodo airfields in Norway, but it didn’t look like we had the fuel to get to either, let alone have enough to make a landing pass.”
Just as Osterheld started speculating how long he could survive in the freezing water below, Matthews spotted the KC-135Q tanker.“We had less than 10 minutes’ fuel remaining when we hit the tanker,” he said. “The tanker folks were just magnificent.” Since Blackbirds operated over Europe from RAF Mildenhall in England, still several hundred miles to the south at that point, 974 remained with the KC-135 during its homeward flight, refueling so many times that the tanker was close to empty when they touched down.
The crew of 974 was not the first to experience an intake unstart, but no one could understand how this particular mishap occurred. The SR-71 had originally been equipped with an analog computer, and it was possible for the environmental inputs to get ahead of the controls, which would cause an overload and shut down the spike. The early computers were later replaced with digital models, but the unstart problem persisted.
“Each of the SR-71s was a completely different airplane from the others,” Osterheld pointed out. “They were handmade, and all they really had in common was their overall configuration. Nine-seven four had previously had a reputation as a nice-flying Blackbird, but that changed after this mission.” After four days of intensive systems maintenance by Lockheed contractors at Mildenhall, the only thing anyone could say for certain was that it seemed to be a heat-related anomaly that was difficult to troubleshoot on the ground. “Anomaly” is a word no mechanic or technician likes, because it means the problem is essentially unsolvable.
With its engine control system thoroughly checked out, 974 was ready for the Baltic run its crew had aborted—a challenging mission that involved “threading the needle” over the Skaggerak between Denmark and Sweden in order to remain in international airspace, which could only be done at lower speeds. Over the Baltic the SR-71 would be limited to a maximum speed of Mach 2.8 as it made banking turns with the wings canted 45 degrees— sharp and steep for an SR-71—to remain within the confines of international airspace. Because the inlets were not optimized for Mach 2.8 flight, unstarts were not uncommon in this situation.
Again 974 approached the reconnaissance track at 83,000 feet. As Matthews brought the aircraft up to speed for the run once more, they again lost the spike on the right engine. This time he managed to effect an auto-restart, but they had to abort the mission a second time. “The first time, they’ll accept that it’s a mechanical glitch,” Osterheld explained.“But if it happens a second time, with the same crew, they start to think it might be a human-factor problem.” Back at Mildenhall the crew went over everything and saw nothing amiss. Now the anomaly was classified as an “unknown problem.”
The final mission of the deployment loomed: a return to Murmansk, with the “carrot” that once the leg was completed the crew could head directly to Beale AFB in California. “We made the Barents run and got what they wanted, then looped around and headed for home,” Osterheld said. “We were looking at a two-hour transatlantic crossing, with a refueling when we got to Nova Scotia and then another two hours across the continent to Beale.”
Over Nova Scotia, 974 hooked up with a new KC-10 Extender tanker and took a long drink of JP-7 fuel. Then the SR-71 unhooked, turned and accelerated to return to cruising altitude and a final run for home. “All of a sudden, our suits blew up—we’d lost pressurization!” said Osterheld. Since the Blackbird was unable to go supersonic without the necessary pressurization, he contacted the tanker, relaying word that 974 would be accompanying the KC-10 on the trip home.“So, instead of a quick four-hour flight, we were sitting in there for 10½ before we got back,” he said. “That’s a very long time in those hard helmets.”
Six months later in a different SR-71, Osterheld and Matthews experienced what at first seemed like another emergency near Murmansk. “We were briefed that there was a possibility the Soviets might do more than track us, that they might attempt a launch,” Osterheld said. “We were told to keep monitoring the HF warning radio from SAC while they kept track of Soviet activities.” With this in mind, the RSO paid close attention to the electronic defense system as they rounded Novaya Zemlya and headed toward the Kola Peninsula. “In the winter at that altitude, the sun is very low on the horizon, so I had the sunscreen pulled up on the left side,” he recalled, referring to a plastic screen that pulled up from just below the window and attached above it with Velcro. “The defense system told me we were being painted, and this time it was of longer duration, less like a training mission and more like a potential launch. I started thinking to myself what would happen if they held that track and did fire an SA-5. I looked at the clock on my instrument panel and just at the moment I was thinking that if they had fired, the missile would be arriving, all of a sudden the Velcro came loose on the sunscreen and it snapped down and I got this bright flash of sunlight. I was absolutely certain for a second or two that they had launched and that was the explosion.”
Osterheld’s foot happened to be on the intercom switch at the time, and his warning shout startled the pilot, who responded, “What the hell?” “I realized as I shouted my warning what had happened,” said Osterheld, “so I was yelling, ‘Disregard! Disregard!’ We got back on track and finished the mission. Looking back it was pretty funny, but right at that moment I thought they had nailed us.”
Like most who were privileged to fly in the SR-71, Osterheld’s enthusiasm for the technologically advanced aircraft is obvious. “Just building the airplane was difficult,” he said. “It was 90 percent titanium, and they had to develop an entire technology to work with that. They couldn’t use tools with chromium because they would contaminate the structure. Once a year Palmdale would put fluoride in the water, and they discovered after the first time that happened that they had to stop production while that was going on because using water with fluoride in it could contaminate the metal. The main gear leg was the most complex titanium forging ever made.” Ironically, 93 percent of the titanium used in building the Blackbird came from the Soviet Union, at the time the world’s largest supplier of the rare metal.
“Everything about the SR-71 was designed to beat the heat problem,” Osterheld explained. Its special 22-ply tires, for example, were aluminum-impregnated to protect them at speed.“They were inflated to 425 psi with nitrogen because it was inert, and they were only good for 15 landings.” Outside heat limited the aircraft’s operation, from its maximum speed to how long it could maintain that blistering pace. “Just outside the cockpit windows at Mach 3.2 it was 525 degrees Fahrenheit,” Osterheld noted. He said that crews would take the “beef stew” meal they were sometimes given—which came as a paste inside a toothpaste tube, just like astronauts’ food—and hold the tube near the window for a minute or two to heat it before eating. “You always had to be careful, though, about taking your eyes off the instruments for any length of time,”he added.“The airplane knew when you weren’t paying attention, and that was when the master caution light was most likely to come on.”
Osterheld pointed to the SR-71’s control system as an other of its remarkable features. “It wasn’t a fly-by-wire system, it was old-fashioned cables and pulleys,” he said.
As the Blackbird’s speed and outside temperature increased, there had to be a way to maintain proper control reactions to the pilot’s control inputs.“Back in the rear, there was a device we called the ‘mixer,’ a control system designed and built by the Bulova watch company that could translate inputs from the control stick into offsets of the elevons that were appropriate for our speed. Additionally, the airplane expands one or two inches when it’s at Mach 3, which would make the control cables problematic, except they put links of titanium in the cables that would expand and contract with the heat. That way you got the same control inputs whether you were flying subsonic or at maximum speed.”
Designed before inertial navigation systems (INS) became common, the SR-71 needed a navigation setup that could be used world wide, to provide more accurate information than anything else then in operation. The answer was an onboard astro-inertial navigation system (ANS) that could track specific stars.“The computer had up to 61 different stars that could be used, depending on where in the world we were flying,” explained Osterheld. “There was a small telescope on an inertial-stabilized platform dead center of the airplane. It was so sensitive that when we taxied out of the barn at Beale AFB, by the time we got to the runway for takeoff it had tracked and set the stars. The system could guarantee accuracy anywhere in the world to better than 300 feet of course track at 2,200 mph.”
On one of Osterheld’s flights with Matthews, the pilot asked his RSO if they were over the ocean. “The system said we were right on course,” Osterheld said. “I looked out and saw all the ice below. Visually, you couldn’t tell where the ocean ended and the land began, which was what had concerned Joe. We couldn’t have flown that mission with any other navigation system.”
While there isn’t a lot of weather above 60,000 feet, the Blackbirds could still be affected by conditions near the surface. “The weather wasn’t as benign as they say,” he noted. “In the summer, when it was warm down below, the airplane flew less efficiently at altitude because the air was relatively warmer. We had a slower climb and got to maximum inlet operating temperature before we’d hit Mach 3.2. Conversely, in the winter, when it was cold down below, our performance was enhanced. We could pull contrails at 83,000 feet, and be at maximum speed in mid-burner.”
Surface weather could also cause problems for the Blackbird over the Korean Peninsula.“We would fly west to east across the peninsula, and when we got over the Sea of Japan there was a surface turbulence that would create a short-cycle chop at 72-73,000 feet,” he said.“In the cockpit, out on the end of that long fuselage, it was like bouncing up and down on the end of a diving board. It would frequently kick off the autopilot, and the pilot would have to take manual control.”
SR-71s crews flew in David Clark pressure suits that were for all intents and purposes spacesuits. “Wearing the suit was like putting on a sleeping bag,” Osterheld remembered. “The one problem was the helmet. On a long sortie, like the combined Murmansk and Baltic run, the neck ring would bother you because you could only rotate your head side to side. One good thing with the drink bottles was we could insert them into the helmet port, and they were long enough you could maneuver them to be able to scratch your nose.” If internal cockpit pressure failed and the suit inflated, “you were like the Michelin man, you struggled to move.” At that point the mission had to be aborted and the airplane descended below 25,000 feet.
Osterheld’s time in the Blackbird, from 1983 to 1987, coincided with its final days as America’s premier reconnaissance platform. Although disappointed by the program’s cancellation, he and the other crewmen are proud they could fly the most advanced airplane ever built. “The one thing I remember the most was the dedication of the ground crews, both the blue-suiters and the Lockheed contractors,” he added. “We wouldn’t have accomplished anything without them.”
In a sad postscript to the story of Blackbird 974, it crashed into the South China Sea after an engine exploded on April 21, 1989, the last of three SR-71s lost in accidents. Its pilot, Lt. Col. Dan House, and RSO Lt. Col. Blair Bozek both ejected safely and were rescued.
Thomas M. Cleaver last wrote for Aviation History about the Grumman OV-1 Mohawk (September 2012). Additional reading: Flying the SR-71 Blackbird: In the Cockpit on a Secret Operational Mission, by Col. Richard H. Graham, USAF (ret.); Lockheed SR-71: The Secret Missions Exposed, by Paul F. Crickmore; and Skunk Works: A Personal Memoir of My Years at Lockheed, by Ben R. Rich and Leo Janos.
Originally published in the May 2013 issue of Aviation History. To subscribe, click here.