Figure 9
No book on the SR-71 would be complete without an understanding and appreciation of just how valuable the KC-135Q tankers and their crews were to the successful and safe completion of every sortie. The KC-135Q model tankers were unique within the Air Force and therefore earned the Q-model designation. At Beale, there were a total of 35 Q-model tankers and two squadrons of crew members supporting the SR-71’s worldwide operation. In the mid-1980s, we began using KC-10s as additional tankers.
The Beale tanker crews went TDY to Okinawa and Mildenhall with SR-71 crews. There, we all worked, lived, and partied together. Because of the extensive TDY commitment, Beale tanker crews did not sit on SAC’s nuclear alert like other KC-135 tanker crews. They were grateful for this exception, as it made them feel extra special among SAC tanker crews, and they were.
A bond developed between tanker and SR-71 crews that didn’t exist elsewhere in the Air Force. The tankers took considerable pride in their work because of the exclusive SR-71 refueling mission. They knew, and so did Habus, that mission success was directly related to their ability to refuel the SR-71. They were always there, in the murk and dark of night, with a full load of JP-7 waiting for the SR-71’s arrival. It was comforting to have tanker crews who knew us well doing the refuelings. There has never been a missed air refueling in the history of the SR-71 program; they were always there. On several occasions, tanker crews flew well outside their air refueling track to rescue an SR-71 in trouble. All Habus owe them a debt of gratitude for being there!
The KC-135Q crews and their aircraft were unique from the rest of the Air Force in several other ways. Their air crews were the only crews certified in our radio-silent rendezvous procedures, and their boom operators were the only operators qualified to refuel the SR-71. Anytime an SR-71 was airborne anywhere in the world, there had to be a tanker either in the air nearby or on the ground ready to launch ASAP in case an SR-71 reached a critical fuel state on the return leg. The Q-model tankers had special plumbing between their fuel tanks, allowing them to move both JP-4 and JP-7 fuel between various tanks. Their engines could burn either JP-4 or JP-7. If the SR-71 landed where JP-7 was not available, the Qs had to ferry the fuel in. Ground refueling the SR-71 directly from the KC-135Q was accomplished by a transfer hose between the two aircraft.
Second only to fuel, the ARC-50 radio was the most important item aboard the tanker. If the tanker and SR-71 were on the same UHF frequency and had the correct codes set in their modems, they had ranging and bearing to each other. Over the open ocean, it was not uncommon to pick up the tanker at ranges of three hundred nautical miles or greater.
When tankers flew in formation, they were referred to as a “cell.” Depending on the amount of JP-7 to offload, there would be two, or sometimes three, tankers in a cell. Typically, the SR-71 received gas from two tankers (called a “split offload”) and used the third tanker as an airborne spare. The spare provided redundancy in case either of the other two was unable to transfer fuel or had to abort for an in-flight emergency. In the early 1980s, money for tanker flying time started to become tight, so SAC reduced the number of tankers to refuel the SR-71 to the minimum necessary—often only one!
The rendezvous with the tankers was one of two types. A “hot” rendezvous originated from a high-Mach cruise leg and supersonic descent, while a “cold” rendezvous was a subsonic arrival, generally after takeoff. For this mission, our first refueling will be a cold one. Normal refueling altitudes were typically between twenty-five thousand and twenty-eight thousand feet.
During every refueling, there was a minimum amount of fuel established that told the crew when to divert to an alternate base to land called “bingo” fuel. Bingo fuel was computed so the crew could rendezvous with the tanker at the ARCP, fly forty nautical miles down the refueling track attempting to get fuel, and, if unable, divert to the alternate air refueling base and land with 7,500 pounds of fuel remaining (peacetime) and with 5,000 pounds otherwise. It may seem like a lot of fuel remaining at destination, but when you consider a missed approach and standard instrument landing for a thirsty SR-71 burns around three thousand pounds of fuel, that’s not much fuel in reserve. Pulling up from takeoff for a short visual downwind pattern to a full-stop landing burns over one thousand pounds of fuel.
In theory, whenever crews computed they would be below bingo fuel, they were supposed to abort the mission and proceed to the alternate landing base. In reality, most Habus took an educated gamble rather than abort a mission. As long as the refueling and alternate weather were good, it was a gamble worth taking. If crews knew they were going to be below their air refueling bingo during cruise, one option available was to call the tankers prior to descent and have them move the ARCP closer to the SR-71’s inbound descent track, saving precious fuel. However, this option was not always available.
At one time or another, practically every Habu was below bingo fuel, searching for the tankers in nasty weather, knowing only too well the alternate base(s) was right at weather minimums: not a pleasant feeling! Once the SR-71 crews visually sighted the tankers, they were anxious to hook up. The sweetest words Habus in this predicament ever heard were boom operators saying, “You’re taking gas.” An immediate sigh of relief usually followed from the cockpits. The tankers were our lifeline; they knew this and accepted the responsibility with pride.
The SR-71’s air refueling system could receive fuel at a maximum rate of approximately six thousand pounds per minute. All six tanks could be filled in about fifteen minutes at a refueling pressure of sixty-five to seventy psi. Once hooked up and transferring fuel, the boom automatically disconnected whenever the fuel pressure exceeded seventy psi. This was the normal disconnect procedure for full tanks and was called a “pressure disconnect.”
The refueling for this mission is planned to occur at twenty-six thousand feet. The tanker cell is in a left-hand orbit in the air refueling track at twenty-seven thousand feet thirty minutes prior to the SR-71’s arrival. The SR-71 will be at twenty-five thousand feet (two thousand feet below the tanker’s altitude) by at least forty nautical miles from the ARCP as it continues to close at Mach 0.9. Once the lead tanker begins ranging on the SR-71, the tanker navigator starts timing and controlling the length of their racetrack legs, planning to end up precisely abeam the ARCP when the SR-71 is about fifteen nautical miles out from the ARCP. The lead tanker navigator used timing charts based on the distance between the two aircraft to help compute when to make the final turn for join-up.
When the time was right, the lead tanker navigator had his pilot begin the final 180-degree left turn, planning to roll out about three to four miles directly in front of the SR-71. With range and bearing information to the tanker, Habus were allowed by the book to continue the rendezvous down to one mile in the weather before the pilot had to visually see the tankers. To get their precious load of gas, many Habus have opted to continue the rendezvous with visibilities below one mile.
If everything was proceeding normally, the tankers initiated their descend and accelerate maneuver when the SR-71 was one mile behind them and still closing at Mach 0.9. The maneuver called for the tanker cell to add power, descend one thousand feet, and accelerate to 325 knots. Habus remained at their altitude (one thousand feet below the tankers) until sighting the tankers visually, then slowly moved in and up to the precontact position.
Not every rendezvous went smoothly. On a hot rendezvous, if the SR-71 crew initiated its supersonic descent too late, or the tanker crew made its final turn too late, it was possible to end up with what was called a “tanker overrun.” In an overrun scenario, it was highly probable that the SR-71 would end up in front of the tankers rather than behind them. When an overrun was called out over the radio by the tanker or SR-71 crew, the procedure was for the tanker to descend and accelerate immediately and the SR-71 crew to slow down as much and as quickly as possible. The SR-71 pilot could often do S-turns to help increase the distance between the two aircraft. In any case, the rendezvous eventually sorted itself out.
While the pilot was taking on fuel, it was practically impossible for him to check anything in the cockpit. Flying the SR-71 in the correct refueling position required a considerable amount of concentration outside the cockpit. Prior to reaching the ARCP, the SR-71 crew completed the following checklist so the pilot could focus his full attention on flying:
1. CG—Checked
During the initial portion of refueling, the center of gravity moved aft slightly. The pilot made sure that it was far enough forward to stay within subsonic limits so he wouldn’t have to deal with the CG during refueling. The pilot confirmed, “CG at seventeen percent.”
2. Windshield deice—Set
If icing conditions were anticipated, the pilot turned the windshield deice switch to the ON position and said, “Windshield deice on.” Strangely enough, only the left windshield received hot air for deicing.
3. Refuel switch—AIR REFUEL, READY light on
Moving the switch to the AIR REFUEL position opened up the air refueling door and turned the cockpit READY light on, indicating that the system was ready to lock onto the boom receptacle. The pilot stated, “Air refuel, ready light on.”
4. Tank 4—Press on
This step ensured a continuous flow of fuel to the engines during refueling from a fuel tank that was relatively neutral in moving the CG. The pilot stated, “Tank four on.”
5. IFF—As required
When two aircraft are in close proximity, they produce erroneous and confusing signals if both transponders are on. Normally, the lead tanker was squawking (transmitting) with the IFF transponder, requiring the RSO to turn the SR-71’s IFF off, saying, “IFF off.”
6. Forward xfer—OFF
A reminder for the pilot to terminate the forward transfer he might have started in step one. He replied, “Forward transfer off.”
7.* Interphone—Set
Most crews stayed on hot mike during refueling so the pilot and RSO could talk to each other without having to engage the mike switch. Both pulled the in-flight refueling COMM monitoring button upward, allowing interphone communications between the tanker crew members and the SR-71 crew once the tanker’s air refueling nozzle was locked into position. It was a unique, secure feature that allowed anyone to talk during the refueling and pass along information that made the job run smoother. Both SR-71 crew members stated, “Interphone set.”
This step made sure both navigation sets were not in the air-to-air mode, allowing the RSO to use either TACAN set for position information. The pilot and RSO confirmed, “TACAN T/R.”
9.* Radios—Set
The crews checked to make sure they had the correct UHF and VHF frequencies set so they could communicate with the tankers if necessary on either the primary or secondary frequency. Both stated, “Radios set.”
10. Anticollision lights—FUS
To prevent the boom operator from being distracted by the SR-71’s bright, rotating, anticollision lights on top of the fuselage, the pilot placed the light switch in the FUS position, which retracted the lights and illuminated steady white lights. The pilot stated, “Anticollision lights fuselage.”
11. (Night only) FUS & TAIL—DIM
The boom operator’s night vision was improved if the SR-71’s lights were dimmed. The pilot confirmed, “Fuselage and taillights dim.”
During the last forty nautical miles or four minutes it took the SR-71 to reach the ARCP, the RSO monitored the distance and bearing to the tanker very closely. Although the lead tanker navigator was primarily responsible for a successful rendezvous, RSOs kept a close eye on how everything was progressing. As soon as the pilot had visual contact with the lead tanker, he slowly climbed to the air refueling altitude of twenty-six thousand feet. As he neared the tanker, the pilot slowly decreased his airspeed, reducing his rate of closure. In preparation for refueling, the boom operator lowered the boom from a stowed position to the contact position, letting the pilot know he was ready. The pilot maneuvered the SR-71 to what was called the “precontact” position, about fifty feet behind and ten feet below the tanker’s boom nozzle. Slowing down to the same speed as the tanker, the pilot stabilized the SR-71 in the precontact position.
Every SR-71 pilot lowered his seat as he approached the precontact position, although this was not a checklist item. The upward visibility to watch the tanker’s director lights was very uncomfortable in the normal flying position. To decrease the angle looking upward and accommodate the added weight of the pressure suit helmet, lowering the seat was a must for most pilots. The electric seat height adjustment switch was located on the right-hand side of the seat with a total travel of nine inches.
Both the tanker and SR-71 had radio-silent procedures to follow, letting each other know when they were ready to commence refueling. With the tanker’s boom trailing, a ten-foot extension of the probe meant he was ready for contact. Opening the air refueling door meant the SR-71 was ready. From the precontact position, the pilot slowly maneuvered the SR-71 forward and up to the contact position. Although an experienced SR-71 pilot knew where the contact position was, director lights located on the belly of the KC-135Q gave the pilot clues as to how close he was to the exact position (see figure 9). The boom operator manually controlled the lights. A steady red light indicated a large correction; a flashing red light meant a small correction in the direction indicated by the red lights.
The director lights on the left side of the tanker’s belly told the SR-71 pilot to maneuver up or down, and the lights on the right side were for maneuvering fore and aft. Once the boom nozzle was connected to the SR-71, the director lights worked automatically to let the pilot know how he was doing and what corrections he needed to make. When the pilot was flying well within the limits of the boom, the director lights were green. In the perfect position, the green captain’s bars illuminated on the belly. The captain’s bars were two parallel bars, similar to captain rank insignia, on the left side of the director lights.
Crews inexperienced in air refueling had to learn what many Habus knew instinctively from years of air refueling in other aircraft. Did a flashing red light call for a small or large correction? Were the left director lights up/down or fore/aft? Did the director lights indicate the direction to fly to or from? It could get confusing!
Adding a small amount of power, the pilot moved forward into the contact position. He slowly maneuvered the SR-71 to put the very end of the air refueling boom about three feet outside his front window. Once he stabilized the plane there, the boom operator flew the boom up and back to the awaiting air refueling receptacle. The READY light extinguished when the boom nozzle was seated and firmly latched. Once the boom nozzle was locked into the receptacle, the crews talked over the interphone systems. The first words typically spoken over the interphone were from the boom operator, saying, “Contact. You’re taking gas.”
If the boom disconnected for any reason, the air refueling pushbutton displayed DISC. It was necessary to depress the pushbutton switch to reset the system and illuminate the READY light before the boom could be re-engaged. The pilot was well aware of the location of the reset button and instinctively took his left hand off the throttles, quickly reaching up to push the button to obtain the READY light for another connection.
There were four ways a disconnect could occur. The boom operator could initiate a disconnect. Squeezing the trigger switch on the SR-71 pilot’s stick initiated a disconnect. If the fuel pressure reached seventy psi, the nozzle automatically disconnected. An automatic disconnect occurred if any of the boom’s parameters were exceeded.
The boom’s upper elevation limit was twenty degrees, and the lower elevation limit was forty degrees, before an automatic disconnect occurred. The boom extension limits that caused a disconnect were an inner limit of six feet and an outer limit of eighteen feet, resulting in a total travel of twelve feet of play for the pilot. There was no automatic disconnect in azimuth (left and right), but the limit was ten degrees.
Refueling the SR-71 was easier than it sounds as long as everything went smoothly. It was very stable on the boom and responded quickly to small throttle movements. The pilot merely flew a formation position on the tanker while checking the director lights for confirmation of how he was doing.
Once connected and taking gas, the refueling took place while flying either a racetrack pattern or a straight-line refueling track, depending on the available airspace and where the SR-71 was heading after refueling. Sometimes the tankers had to change altitude or deviate around thunderstorms, making the refueling track unpredictable. The RSO kept his pilot informed as to how much longer they had remaining in the refueling track. He also monitored the tanker’s navigation, since our ANS system was much more accurate, particularly if the tankers were deviating around nasty weather.
During the final stages of refueling with the lead tanker, the second tanker slowly maneuvered into position, getting ready for its turn, one thousand feet above and line abreast of the lead tanker. When the lead tanker advised, “You have your offload,” the pilot took time to thank the tanker crew for the excellent rendezvous and refueling. After stating, “Disconnecting now,” the SR-71 pilot squeezed the trigger to disconnect the nozzle and dropped down and slightly back. Once he was well clear of the lead tanker, the pilot directed his attention to the second tanker.
He maneuvered the SR-71 up to the precontact position and repeated the previous procedures for the remainder of his fuel. Once satisfied the second tanker was capable of transferring fuel, the pilot often disconnected and flew formation with him if extra time remained to the end air refueling (EAR) point. The other option was to remain hooked up and not transfer fuel. Some pilots did that for refueling practice. The goal was to be at the EAR point with eighty thousand pounds of JP-7 onboard; how you got there didn’t matter.
The final stages of filling up were controlled by the RSO telling the tanker how many fuel transfer pumps to use as the SR-71 approached the EAR point. Normal fuel transfer was accomplished with four of the tanker’s fuel pumps operating. By reducing the number down to three, two, and eventually one pump, the rate of fuel transfer decreased accordingly. If the RSO didn’t reduce the number of pumps, the boom would pressure disconnect with less than full tanks—not a good deal if fuel was tight on the next leg. It’s similar to filling your car up with gas. Once it automatically stops pumping at full pressure, you can always squeeze in a few extra pints of gas in the tank by reducing the pressure.
If the mission didn’t call for a full load of gas, the pilot could beg for a few extra thousand pounds of gas for insurance. If the tanker crews had extra JP-7, they were always willing to give more. The pilot reminded the tanker aircraft commander which direction he would be turning after refueling, just so there was no confusion.
As the fuel approached seventy-seven thousand pounds with hot temp devs, the SR-71 often became thrust limited. Pilots could sense this happening when their throttles began touching the military stops more and more frequently just to stay on the boom. This situation required additional thrust from an afterburner just to stay connected. To light the AB, the book answer was to disconnect from the boom, drop back to the precontact position, light one AB, trim the aircraft up, and move back into the contact position. Forget all that! Every pilot learned to safely place the left throttle in minimum afterburner while still locked onto the boom.
By using the same AB each time, pilots could anticipate the same yawing motion created by the additional thrust and put in about ten to fifteen degrees of left bank to compensate for the yaw. Although Habus had to refuel with the SR-71’s flight controls cross-controlled (right yaw and left aileron) during those last few thousand pounds of fuel, it was not an extremely uncomfortable feeling from the front seat—just a little weird! The left AB was used because the left windshield was the only one that was deiced and might be the only window available to see out of if icing was encountered. Using the left AB was a Habu technique, not an official procedure.
Two other lesser used techniques were available when the SR-71 became thrust limited. The engine’s EGT could be manually up-trimmed prior to boom contact, adding additional thrust. However, the possibility of exceeding the emergency temperature limit of 830 degrees Celsius or compressor stalling the engines was also increased. A third option was to request the tanker to initiate a toboggan maneuver. By establishing the tanker in a shallow descent, it required less thrust from the SR-71 to stay on the boom.
If, for some reason, neither the tanker nor the SR-71 was able to initiate a normal disconnect from the boom, a brute-force disconnect was the only option. The latch-and-toggle hydraulic system incorporated a pressure-relief valve that permitted the boom to come out when a pullout force of approximately 5,400 pounds was applied. The SR-71 pilot placed the air refueling switch in the manual override position (MAN O’RIDE), depressed the trigger disconnect on the control stick, and proceeded with a brute-force disconnect by very slowly backing out in an aft and downward direction.
Typically, a pressure disconnect occurred at the EAR point. The first thing to accomplish once air refueling was completed was to raise the seat back to a normal sitting position. Once clear of the tankers, the pilot selected roll autopilot and AUTO NAV to start the aircraft heading to the next destination point. The pilot asked for the post–air refueling checklist next.
12. Refuel switch—OFF
The pilot reached up and turned the switch to the OFF position, stating, “Refuel switch off.”
13.* Speeds—Crosscheck & monitor
At maximum gross weight, this step was a precaution to make sure the plane didn’t get too slow. Crews paid close attention to not only their airspeed but angle of attack as well. In the early days of the program, several Blackbirds were lost because of low airspeed and high AOA at maximum gross weight coming off the tanker. Both the pilot and RSO confirmed, “Speeds cross-checked and monitoring.”
14. Precomputed CG—Check
The RSO compared the precomputed CG with the actual CG and stated, “CG checked.” If there were any discrepancies, he manually calculated the actual CG using the fuel quantities in each tank.
15. Pump release—Press, confirm tanks normal
The pilot reached to the fuel panel, released tank four from pumping, and checked to make sure tanks one, three, and six were illuminated and pumping. He said, “Tank four released; tanks one, three, and six on.”
If the fuel crossfeed had been on during refueling, the pilot closed it and stated, “Crossfeed closed.”
17. IFF—Set
Once the SR-71 separated from the tanker cell, the RSO turned on the IFF transponder and responded, “IFF set.”
18. EGT—As required
This step was a reminder to put the exhaust gas temperature back in the automatic mode if it had been placed in the manual mode to gain additional thrust. Another reason to place the EGT in the manual mode was to preclude what was called “ratcheting.” During refueling, some pilots moved the throttles back and forth rapidly to stay in the correct position with the tanker. Repeated rapid throttle movements back and forth through the EGT’s permission-switch operating range could cause the EGT to increase sufficiently to derich the engine. Ratcheting was caused by a lag in the EGT’s thermocouple response and could be avoided by selecting manual EGT. The pilot stated, “EGT auto (or manual).”
19. Windshield deice—OFF
If windshield deicing had been used during the refueling, it wouldn’t be needed much longer. The plane would soon be getting hot enough! The pilot stated, “Windshield deice off.”
20. Anticollision lights—ANTI COLLISION
This step turned the lights back to their bright-red, rotating position for better visibility: “Anticollision lights on.”
21. (Night only) FUS & TAIL—Bright
This step made the lights brighter: “Fuselage and taillights bright.”
22.* Interphone—Set
Crews switched to either hot or cold mike at this time, depending on their preferences. Each crew member stated, “Interphone set.”
23.* ANS distance on HSI—DP/TURN
The pilot and RSO cross-checked the destination point they were navigating to and confirmed that the distance in both cockpits read the same. Both of them stated, “120 NMs to DP seven.”