I had originally intended to post a single article on Lockheed C-5 air refueling, but I have been typing away and see that it is way too long for a single post, so I’ll break it up into two parts. Part 2 will be up in two days.
Air Refueling Procedures
Before we get into the specifics of air refueling a C-5, let’s figure out how the two airplanes find each other and arrive in a position to refuel. The C-5 is intended to be loaded up with the cargo to be moved, then fueled to reach the intended destination or to attain the maximum takeoff weight. If the amount of fuel boarded is not enough to complete the flight, an air refueling mission is planned. When an air refueling mission is required, an air refueling track is reserved and a tanker (either a KC-135 or a KC-10) is assigned to the mission. Air refueling tracks are mini-airways set aside for military use for refueling missions. The military flight planning publications list all of refueling tracks, the altitudes that are available and what agency controls them. Click on the photo to see it large enough to read the information. There are several column labels across the top that we’ll talk a little about. (There is no telling the age of this air refueling track information. Do I need to put a label on it saying “Not For Navigation Purposes” ?)
The first column gives the track identifier. Let’s look at AR106L (East). The next four columns are navigation points that define the track. If you were to plot them on a chart they would define a relatively straight line starting near Hill City, KS and ending east of Rapid City, SD. The column ARIP is the Air Refueling Initial Point, ARCP is the Air Refueling Contact Point. and the other two labels are self-explanatory. CR Plan is the Communications/Rendezvous Plan and references setting for the communications and identification equipment found on the respective aircraft. The remaining columns list the altitudes available, who schedules the track and who handles air traffic control of the aircraft on the track. There is also an ARCT involved with the operation which is not listed. The Air Refueling Contact Time is the time both aircraft are to be at the ARCP. It is established when the track is reserved. (Enough letters for you?)
There are two ways the tanker and receiver manage to find each other. One method of rendezvous is called the Enroute Rendezvous and is simply a navigation point that the two aircraft fly to on a specific heading and at a specific altitude. The method that we most often used in training is called the Point-Parallel Rendezvous.
On a point-parallel rendezvous, the tanker takes off from it’s base, flies directly to the ARCP and enters a left-hand holding pattern. The receiver flies to the ARIP and arrives there at the rendezvous altitude and airspeed. A 3000′ block of altitude is used for air refueling, for example FL200, FL210 and FL220. The receiver will arrive at the ARIP at FL200. In the case of the C-5, the refueling speed is 252 knots. The tanker will be orbiting at the ARCP at FL210 at the air refueling speed. The tanker and receiver will be on the assigned refueling frequency 15 minutes before the ARCT, listening for the other aircraft. Once communication is established and the two aircraft are positively identified the tanker will accept MARSA which means Military Accepts Responsibility for Separation of Aircraft. Without that, ATC would still have the responsibility of keeping the two planes separated. Once MARSA is established, the ATC controller will clear the two aircraft to conduct air refueling on the specified track in the block of altitudes and will clear them to the air refueling frequency.
While the tanker was in orbit at the ARCP waiting for the arrival of the receiver, the crew determined the drift angle required to remain on the air refueling track with the prevailing winds. They use this information and the speeds of the two aircraft to determine an offset from the track and a turn point range. When the receiver calls crossing the ARIP heading down the track the tanker will turn toward the receiver and establish the necessary offset away from the track centerline. When the two aircraft close on each other to the turn point range the tanker will start a left 180-degree turn to roll out on the track centerline. The planned bank angle, turn range and offset will result in the tanker rolling out 1-3 miles in front of the receiver. Pretty elegant when it works out right. A smart receiver pilot will always calculate the turn range and offset on his own and will check the tanker position on the radar/TCAS and will watch the progress as the turn progresses.
Now the two aircraft are in trail, hopefully in visual contact with each other. Well, the pilots of the receiver should see the tanker and the tanker boom operator should see the receiver, but weather conditions may not always make that possible. Now the receiver will close the distance between the aircraft and move to the pre-contact position. The pre-contact position is about a mile behind the tanker and 50′ below it. (If visual contact is not made by the pre-contact position, the refueling mission is aborted and the receiver will divert to an alternate airport.) When the receiver has stabilized in this position, the next step is to make sure the aircraft is ready to accept the fuel. For the C-5 this means running a checklist that results in opening the air refueling door and checking the fueling systems.
Air Refueling the C-5, Getting Ready
Here’s a picture of the C-5 fuel panel at the flight engineers station. The air refueling part is at the top-middle of the panel. The switch on the top left turns on power to the system. The switch on the top right provides emergency operation of the boom latch – toggles that grab the boom when it hits the bottom of the refueling receptacle. The middle switch opens and closes the air refueling door. The bottom two switches open the refueling receptacle to the aircraft fuel system. There are three lights on the little panel. The top one illuminates when the refueling door is not locked closed, the two lower ones are the Ready light and the Latched light. Ready, meaning the system is set to receive fuel and latched meaning the toggles have closed on the refueling boom in the receptacle.
There is a switch/indicator light panel just above the left pilot seat that also has three air refueling system lights, Ready, Latched and Disconnect so that the pilot can monitor the status of the system.
Once the receiver has stabilized in the pre-contact position and the air refueling system is ready, the receiver pilot makes a radio call to the boom operator acknowledging the “Ready” status. The boom operator replies that the tanker is also “Ready” and clears the receiver to the contact position.
We’ll start moving into position in Part 2.