Figure 7
The mobile crew knew as soon as the crew chief disconnected his headset that the crew was ready to taxi. After stowing his headset and cable, the crew chief smartly walked about 150 feet out, directly in front of the SR-71, did an about face, and stood at parade rest. The mobile crew turned the car so they were now looking at the control tower. The tower officer asked the tower personnel to give the steady green “cleared to taxi” light to the mobile car and plane.
When the pilot was ready, he flashed his taxi light to signal the mobile crew and crew chief. The crew chief raised his arms high over his head and crossed them, giving the pilot the visual signal to “hold the brakes.” He immediately followed that with lowered arms to each side and gave the thumbs out signal to his assistants to “remove the chocks.” Each assistant removed the large chocks in front of the main gear and pulled them out of the way. The crew chief put his arms up and gave the fore and aft waving motion for the pilot to add power and slowly begin the taxi. The pilot added a small amount of power to smoothly roll over the cheater chocks—small triangular chocks designed to hold the SR-71 in position at idle power only.
The mobile crew began leading the SR-71 out to the runway. The pilot taxied at a speed that kept him well behind the mobile car. The main purpose of the mobile crew at that point was to look for any objects on the taxiway that could damage the SR-71’s tires or be sucked into the engines. The pilot had to taxi far enough behind to brake if the mobile crew had to suddenly stop to pick up something off the taxiway. It was always a concern for the pilot not to brake any more than necessary because the tires were easily overheated. The idle thrust of the SR-71 on a level taxiway required constant braking to slow it down.
Following behind the SR-71 was a caravan of between two and six maintenance vehicles, depending on how many personnel wanted to watch the takeoff. Many of them were out there to watch the fruits of their labor: the impressive takeoff and climb out. Others watched to make sure their particular aircraft systems passed their final checks.
The one maintenance vehicle required to follow the aircraft out was a large, six-man military pickup truck, modified with steps and a platform in the bed. If the crews had an emergency, the truck drove up to the cockpits, providing them a means of escape. Habus had no means of getting to the ground level from their cockpits without outside help, as the aircraft was over eighteen feet in height.
1. Braking & steering—Checked
During taxi, the pilot tested the brakes on individual hydraulic systems. After disengaging the nose wheel steering, the pilot braked slightly in both directions on the left and right hydraulic systems, checking for proper brake responses and the possibility of dragging brakes. When completed, the pilot stated, “Brakes and steering checked.”
2. Turn & slip indicator—Checked
While the pilot did the brake check above, he also glanced at the turn-and-slip indicator to make sure the needle deflection was correct and the ball was free to move. He stated, “Turn and slip indicator checked.”
3. SAS lights—Checked
The pilot glanced at the SAS panel, making sure the pitch, roll, and yaw sensor lights remained out, and said, “SAS lights checked.”
4. ANS—As desired
The RSO switched the ANS from the INERTIAL ONLY mode and placed it into the ASTRO INERTIAL mode of navigation. The ANS easily achieved star tracking while taxiing out, even on hazy days.
As the pilot approached the departure end of the runway, he taxied slower and followed the crew chief’s visual signals to line up for the engine run. As soon as the crew chief had the plane in position, he extended both arms over his head and slowly crossed them to visually tell the pilot where to stop. The crew chief had to ensure nothing was behind the SR-71, since the engine run was accomplished at full military power. Once the crew chief gave the visual signal for “chocks installed,” the pilot, RSO, and crew chief completed the following steps to ensure the SR-71 was ready for takeoff.
A large majority of the steps were merely rechecking what had been accomplished previously, but these components were considered critical enough to go over one last time. This check was often referred to as the “last-chance inspection.” All of the steps were accomplished with visual signals between the crew chief and the pilot. If circumstances required verbal communication, the crew chief could plug his headset into the interphone panel and talk directly to the pilot or RSO.
1.* ANS distance on HSI—DP/TURN
The pilot looked at his navigation display and crosschecked with the RSO’s distance to the first DP, making sure they were both ready to follow the instrument departure procedure once airborne. Both crew members replied with the displayed distance to the first destination point: “DP one . . . fifteen miles.”
2. Flight instruments—Set
After making one last check to make sure the flight instruments were set up to fly the specified route, the pilot stated, “Flight instruments set.”
3. Engine run—Lockout & EGT trim checked
The engine run involved a rather lengthy check of all engine parameters, one engine at a time.
To signal everything was clear around the SR-71 and he was ready for the engine run up, the crew chief pointed to the left engine with one hand and extended his other arm upward and rotated his index finger. The pilot pumped up each brake and held the brakes tightly as he smoothly advanced the left throttle to the military power stop. Once the throttle reached the stop, he moved it back about one-half inch and returned it to the military stop again. This procedure removed any internal friction (called hysteresis) from the fuel control linkage to the throttle. Although chocks were installed, the pilot had to hold the brakes tightly for over thirty seconds on each engine while the static parameters were recorded by the aircraft’s mission recording system (MRS) or the newer DAFICS. This really tested the leg muscles!
At full military power, the pilot watched for a COLD flag to appear in the EGT gauge if the temperature was below the nominal trim band. The nominal EGT trim band (see figure 7, Engine Automatic Trim System) and engine rpm were calculated prior to the mission briefing. For inlet temperatures above 40 degrees Celsius, which they definitely were during Mach 3+ cruise, the nominal EGT trim band was between 790 and 800 degrees Celsius. If the EGT was above or below these values, an electric trim motor for the respective engine regulated its main fuel control and automatically provided EGT within a 10-degree Celsius deadband.
The pilot reached outboard of the throttle and lifted the left EGT switch out of the AUTO EGT position to the HOLD position and momentarily moved it aft to manually down-trim the EGT below the deadband. Then he placed the switch back to the AUTO EGT position to make sure the COLD flag appeared on the gauge and that the automatic EGT trim system trimmed the EGT back into the deadband.
While the engine was still at full military power, the pilot checked to see that the inlet guide vane (IGV) light remained off. He then reached for the IGV lockout switch and moved it from the LOCKOUT position to NORM and observed the left IGV light illuminate, indicating that the IGVs shifted from cambered to axial. If the IGVs didn’t shift during this check, it was an automatic abort.
The pilot gave the left engine gauges a quick scan for normal indications at full military power. After he accomplished all the above checks, the pilot slowly retarded the throttle and checked that the IGV light extinguished as he brought the throttle back to idle power. If everything checked satisfactorily, he gave the crew chief a thumbs-up and waited for him to proceed in front of the right engine, repeating the same process.
4. EGT trim switches—HOLD or AUTO
If the EGT trim was not working properly in the AUTO position, the pilot moved the trim switch to the HOLD position, where he manually controlled the EGT. If the trim was working normally, the pilot stated, “EGT trim AUTO.”
5. Flight controls & trim—Check
Watching the crew chief for visual confirmation, the pilot accomplished another complete flight control check. The pilot made a quick scan of the flight control hydraulic pressure (A and B) systems, making sure they were reading normally and then glanced at the trim indicators for each axis, checking they were all reading zero (neutral). The pilot stated, “Flight controls and trim checked.”
6.* Fuel sequencing—Checked
Fuel tanks one, three, and five (or six, depending on the fuel load) should have been illuminated on the fuel panel and the quantities decreasing from their initial readings. The pilot and RSO both stated, “Tanks one, three, and five on and decreasing.”
7.* CG—Checked
For takeoff, the CG had to be less than twenty-two percent. If the CG gauge was reading greater than twenty-two percent, the pilot turned the forward transfer switch on to move fuel forward into tank one. A center of gravity of nineteen percent was ideal. The pilot and RSO stated, “CG nineteen percent.”
8. Forward transfer—OFF
This step was a reminder to turn the fuel-forward transfer switch off from the previous step. The pilot stated, “Forward transfer off.”
9. Derich—ARM
The pilot took a quick glance to make sure the derich switch was in the ARM position and stated, “Derich armed.”
10.* No. 1 & No. 2 oxy—ON and checked
The pilot and RSO verbally confirmed with each other that their respective oxygen systems were latched in the ON position and the pressure checked. Both crew members stated, “One and two oxygen systems on and checked.”
11.* Bailer bar—Latched & locked
This was a final check to make sure both crew members had previously lowered their glass faceplates and locked the bailer bars to start the flow of one hundred percent oxygen. Both stated, “Bailer bar latched and locked.”
12. Brake switches—DRY/WET & ANTI-SKID ON
The pilot made sure the DRY/WET brake switch was in the correct position, depending on existing runway conditions, and that the ANTISKID switch was on. The normal response was: “Dry, antiskid on.”
13.* Takeoff data—Review
The pilot and RSO looked over their takeoff and landing data cards (see figure 8, Takeoff and Landing Data Card), reviewing the numbers for the takeoff acceleration check speed, refusal speed, rotation speed, takeoff speed, and single-engine speed. The acceleration check speed was the speed the aircraft should have (or exceed) at a given distance down the runway. If the speed was less than the check speed, something was wrong, and the pilot had to quickly decide to continue or abort the takeoff. The refusal speed was the maximum speed the aircraft could accelerate to and still stop on the remaining runway. Rotation speed was when the pilot began to initiate back pressure on the stick to slowly lift the nose wheel off the runway. At takeoff speed, the SR-71 should be airborne. If an engine were to flame out on takeoff, the single-engine airspeed was the minimum airspeed to fly. The response from both the pilot and RSO was: “Takeoff data reviewed.”
14. Pitot heat—ON & checked
After receiving the visual ground signal from the crew chief, the pilot turned the pitot heat switch on. As soon as the crew chief felt the pitot tube getting warm, he gave the pilot a thumbs-up. The pilot replied, “Pitot heat on and checked.”
15. Battery switch—BAT
There was another double check to ensure the battery was connected to the electrical system. The pilot stated, “Battery switch on.”
16. Instrument inverter switch—NORM
The instrument inverter provided emergency AC power directly from the battery to operate critical components for safety of flight in the event both generators failed. This step was to ensure the switch was in the normal position, and the pilot stated, “Instrument inverter normal.”
17. INS altitude—Update
This reminded the RSO to update the INS altitude to the sustained or mid-altitude expected after takeoff. He stated, “INS updated.”
18. VHF ant cover—Removed
The VHF antenna had a protective cover on it. It was fragile and located on the bottom left side of the fuselage, where it could be easily damaged by ground personnel or equipment. The crew chief held up the VHF antenna cover to show it was removed and received thumbs-up from the pilot. The pilot stated, “Antenna cover removed.”
The crew chief checked the tires and brakes. If he found that they had overheated during taxi, the Habus had to wait until the crew chief said they had cooled down sufficiently. At this point, the SR-71 should have had no access panels open, protective covers installed, or any leaks other than the fuel. The SR-71 is the only plane where pilots never accomplished an exterior inspection; maintenance did. Once the crew chief was satisfied that everything checked out, he positioned himself slightly to the left of the SR-71 and waited at parade rest. When he received the final thumbs-up from the pilot, he gave the visual signal to his assistant crew chiefs to remove the chocks from the wheels.
Quite often, the wooden wheel chocks became lodged into the concrete from the forward thrust of the SR-71’s massive engines. In order to remove the chocks, the assistant crew chiefs used a huge sledgehammer to bang away on the ends of the chocks to dislodge them. I always found it ironic that the world’s fastest and highest flying plane, as well as the most complex aircraft of its day, had to be freed up to fly by using sledgehammers.
After the chocks were removed, the crew chief and pilot exchanged salutes. The crew chief and his assistants headed back to their maintenance vehicle while the SR-71 waited for takeoff. Several minutes before the appointed takeoff time (0800), the mobile crew drove up short of the runway and watched for the green light-gun signal from the tower.
With binoculars the tower officer knew precisely how things were progressing at the end of the runway and politely asked the tower personnel to give the waiting mobile car and SR-71 the flashing green light. With about a minute or two to go, the flashing green light signaled the mobile crew to drive onto the runway and gave clearance for the SR-71 to take off when ready. The mobile crew proceeded on the runway to check for FOD the entire takeoff distance. While the mobile crew was busy driving down the runway, the pilot added a touch of power to taxi into the takeoff position and align the SR-71 directly down the runway centerline, braking to a stop.
