Sometimes trust is all we have. But whom (or what) should we believe in?
Bingo Fuel. It was a caution light none of us had seen previously, at least not while operating the CQ-24A Unmanned K-MAX aircraft. With the vehicle many miles from home base, the light was a real concern: it signified a minimum fuel state for the return flight, the words on the command tent’s big screen for all to see.
I was directing a team of contractors testing the K-MAX’s ability to deliver cargo while operating autonomously, part of our workup before we began flying actual missions. We were in southwestern Afghanistan, watching the operator maneuver the aircraft over Forward Operating Base Payne miles to the south of us. Because the K-MAX was over the horizon, the operator was using the Beyond Line of Sight (BLOS) datalink.
Maneuvering manually under BLOS was nonstandard, but I had directed it as a contingency in case the Payne equipment, operated by two Marines we had previously trained, became inoperative. We already knew that the K-MAX could autonomously complete a flight, but I thought it useful to know if we could reposition manually if asked to do so by the landing zone controllers. After all, this was a war zone—stuff happens.
We soon discovered that manual control of a hovering, over-the-horizon aircraft was difficult work. The CQ-24A BLOS installation had the same limitation as any other: system lag. Once a control input was made from our command tent, it could take up to six seconds for the signal to bounce off an orbiting satellite, travel down to the aircraft, influence its vector, send the resulting change in attitude, speed, and position back up to the satellite, and then back down to the operator’s graphic user interface (GUI) screen. (This provided team members with the rare opportunity to complain about the speed of light.)
With this lag, it was quite easy to “chase” the aircraft. Our eventual technique was to make a one-second input on the hand controller, release, then wait until we saw the K-MAX’s icon stop on the GUI screen. Repeated as necessary, the process was as tedious as it was inefficient.
Further, the BLOS installation was so basic that there was no guarantee a one-second displacement on the hand controller would produce the same amount of aircraft movement each time. And without external cameras, the operator had to surmise his entire closed-loop feedback from the GUI screen.
More Than a Fancy Science Project
The Unmanned K-MAX had begun as a mere science project years before. The brainchild of Greg Lynch, a Lockheed Martin program manager and former Air Force helicopter pilot, he first fought his own superiors and then Department of Defense officials over the feasibility of an unmanned helicopter delivering supplies to remote locations in a combat theater.
Lynch believed the K-MAX was the perfect platform for this, an aircraft already proven by hundreds of thousands of manned flight hours. The K-MAX design was simple for a helicopter, which meant it was reliable to the extreme. It was also quiet. Its dual intermesher configuration didn’t require a tail rotor, making its aural signature among the lowest in the world.
The Unmanned K-MAX prototype, using off-the-shelf components, began winning the hearts and minds of executives and officials alike through a series of successful demonstrations, culminating in a final test in 2011. By this time, the United States had absorbed significant ground convoy casualties in its two war zones. The military saw the ground convoy as the primary method of satisfying the logistical needs of the warfighter—and our adversaries saw them as targets with high rewards and low risks.
With the military eager to “get supplies off the roads,” nearly overnight the fancy science project gathered sufficient momentum for the Marines to send it to Afghanistan, as is, with civilians as its maintainers and half of its operators.
In the command tent, the GUI had been slaved to a large TV monitor, which allowed all to see the Bingo Fuel caution light now glowing in bright amber on the left side of the screen. Though it was late December, the temperature in the tent rose perceptually. As the team lead, I wanted calm. I asked the operator, “What does the manual say?”
The system engineer at the back of the tent interjected, firm in his opinion that the K-MAX should depart for home base immediately. I ignored him. I wanted to keep to procedure, seeing this as a good training opportunity. Our real missions had yet to begin, and it was unclear how the team would perform outside the benign and rigidly controlled flight-test environment. The fact that the engineer was not a pilot also mixed into my soup.
The CQ-24A’s operator’s manual had 10 pages of advisories, cautions, and emergencies. After a few seconds of looking, the operator found the entry. “It says that fuel remaining is insufficient to complete the mission without consuming fuel reserves. Abort the mission.”
Abort the mission. It sounds simple, but it wasn’t. First, the K-MAX had to ascend vertically to its preprogrammed departure altitude, in this case a previously coordinated 1,500 feet AGL (above ground level) to avoid other Payne traffic.
The operator could have allowed the aircraft to ascend autonomously, but in that mode the climb rate was anemic. It was standard procedure to use manual mode with its higher vertical-velocity limits, which is what the operator did. Because of the system lag, he overshot his 1,500-foot perch slightly, which was acceptable, but still the climb had taken nearly 90 seconds, all while the Bingo Fuel light appeared to grow brighter.
Once the K-MAX stabilized, the operator announced “Depart” while simultaneously mashing the appropriate hand-controller button with his thumb (in tune with the science-project nature of the program, the controller was a reconfigured Xbox device). We watched the aircraft’s GUI icon skip forward and gather airspeed onscreen, slowly leaving its wind line and pointing NNE for home.
The GUI had a winds aloft indicator and, as the aircraft climbed further into the Afghanistan sky, we could see a substantial headwind component developing for the return flight. Carrying a not insignificant 2,500-pound external payload, the CQ-24A’s maximum airspeed was 80 knots, which then meshed with the wind component to produce an anemic 59 knots of ground speed. This meant the return voyage would consume nearly an hour, a long time to be visually bombarded by the steady amber message: Bingo Fuel.
The aircraft had barely settled into cruise flight when the BLOS connection icon went gray, indicating the datalink was down. Until the link was reestablished, we would receive no further information from the K-MAX nor could we give it commands. Loss of BLOS was a common occurrence as it was dependent on the randomness of the satellite constellation orbiting the earth. Some satellites were stronger and newer than others. Others were inoperative. It was a heavenly crap shoot.
Though we couldn’t see it, we were confident the K-MAX had settled into its autonomous return. We also knew that the Bingo Fuel situation would unlatch itself if the onboard brain determined the conditions had improved sufficiently.
While we waited for the datalink, we considered jettisoning the load, which would have allowed the aircraft to accelerate to its unloaded maximum speed of 100 knots TAS (true air speed). I decided against it. While the aircraft may dip into its fuel reserve, it was not in danger of flameout and the amount of adverse publicity generated by a jettisoned load could set the Unmanned K-MAX Program back before it had really begun.
I made this decision even though I was unsure precisely how much fuel the K-MAX had onboard. To save cost and time, its brain did not take a direct reading from the single fuel tank. Instead, the fuel onboard was estimated by algorithm. While that calculating process had been quite accurate in flight testing, the aircraft’s fuel state was just another sliver of uncertainty weighing down our thoughts.
Though we were presently blind, the tone in the tent was mostly calm. The system engineer sporadically voiced his opinions regarding our courses of action, the most prominent being that the aircraft should be directed to land under power at the preplanned recovery point outside our base perimeter.
I knew that putting the K-MAX down “outside the wire” meant a high probability it would be damaged or destroyed. The base was under surveillance by the Taliban, and from my experience on a previous contract, I knew they had a propensity for coming out of nowhere to wreak havoc on a grounded aircraft.
We waited patiently for our fresh datalink signal. Later, we’d learn to monitor the satellite constellation on a separate laptop, but this early in the deployment we had no way of knowing what was occurring high above our heads. The engineer went mute for a time.
After a few minutes, the datalink restored itself. The K-MAX’s icon began staggering anew across the screen. The amber words remained: Bingo Fuel.
“Put it down at the recovery point. It’s not going to make it home,” declared the engineer.
I had great respect for this man, who was nearly young enough (or me old enough?) to be my son. I had come to value his opinion during flight testing, even staking decisions entirely upon it. But now he was in my realm.
I stepped from the back of the tent and pulled from my pocket the most versatile aviation invention known to mankind: the CPU-26A/P air navigation computer, better known as the E6B Whiz Wheel.
I spun the inner scale under the black pointer until I hit the aircraft’s current ground speed, then read the estimated flight time remaining opposite the distance to be flown. I then repositioned the black pointer to fuel flow in gallons per hour and matched the estimated flight time on the inner scale to gallons to be burned on the outer scale. The output was multiplied by 6.7 to account for the density of JP-8, the type of fuel we were using, and then subtracted from the fuel remaining.
As calmly as possible, I announced, “It’ll land with 200 pounds.”
Coincidentally, this was our minimum landing fuel by directive. The tent went still for good after this. When the K-MAX finally came within range of our line-of-sight antennas, at a spot just short of the outside recovery point, I quickly revalidated my computation. All good.
A few minutes later, we acquired the K-MAX visually, then watched it decelerate for its programmed high hover above the landing pad. The operator wasted no time getting the load on the ground, and then the aircraft itself. It throttled back to ground idle without a hiccup.
When I climbed into the cockpit to shut down the aircraft, I went right to the fuel gauge. Its needle was dead on 200 pounds.
Lesson Learned, Lives Saved
We gathered lessons that day that served us well later. We learned that airmanship was a thing whether the pilot was in the machine or not, but mostly we learned to trust our aircraft. The Unmanned K-MAX blew past its planned six-month deployment in Afghanistan and delivered 4.8 million pounds of materiel, mostly under the cover of darkness, over the next 2½ years.
We used this new aircraft in ways never envisioned by the original request for proposal or later concept of operations. We retrograded material with it, bringing payloads from forward bases back to us. We hooked payloads from an unmanned hover. We dropped and picked up on the same sortie.
Above all, we saved lives. According to statistical data, one US warfighter was lost for every 100,000 pounds of materiel moved in a ground convoy. The 4.8 million pounds moved by the Unmanned K-MAX Program equated to 48 men and women who would have otherwise been lost. That number is what it was all about.