‘Things really got exciting when we flew in clouds or at night over the terrain with TFR,’ Paul Ghiron, former USAF F-111 Aardvark pilot.
General Dynamics won the US Department of Defense contract in 1962 to develop a supersonic aircraft under a program called TFX. This airplane, later designated F-111, would be the first in history to incorporate specific design features to make it capable of performing in multiple roles.
The F-111 is the first production airplane with a variable sweep wing—a wing configuration that can be changed in flight. The wing provided outstanding aerodynamic efficiency. With wings fully extended, the F-111 could take off and land in as little as 2,000 feet. With wings fully swept back, it could reach supersonic speeds at high or low altitudes. At high altitudes, the F-111 could fly more than 2.2 times the speed of sound. At low altitudes, the F-111 could fly supersonic speeds hugging the ground with its terrain-following radar (TFR).
What was it like to fly the F-111 at low level with its TFR?
‘During the daytime, flying the Vark at low level was absolutely the BEST way to see the world! We used the Terrain Following Radar (TFR) some, but mostly hand flew during daytime,’ Jim Rotramel, former USAF F-111 Weapons Systems Officer (WSO), recalls on Quora.
‘At night, it was ‘interesting’. We engaged the TFR system and it pushed us over into a 10 degree dive until we were 5000 feet above the ground, when the dive angle increased to 12 degrees before beginning to level off 1,000 ft above the set clearance plain (how high you wanted to fly above the ground, usually 1,000 ft). After leveling off at 1,000 ft, you could ‘step down’ to as low as 200 ft. The plane was capable of flying Mach 1.2 at 200 ft. However, for the most part, at night we flew at 1,000 ft, both as a safety margin and to not scare people and livestock on the ground.
‘Since we usually flew away from populated areas, this usually meant descending into a black hole. The pilot had a radar E-scope display that showed the terrain as it would look from the side with a projection of what the TFR would do to avoid the terrain, while the WSO had a display of the terrain ahead, as if looking down on it. We would talk back and forth to ensure the airplane wasn’t trying to kill us as we navigated to the target.’
‘One time, we were flying through a valley in Scotland and the pilot peeked outside and was a bit unnerved to see the stars disappearing behind the big black shadows of the mountains on either side of us. I think pilots were less comfortable with letting ‘George’ fly the jet than the WSOs, who were used to not being the one ‘in control’.’
‘Always very smooth and almost always reliable right on set clearance (Altitude setting above ground). The plane was definitely in its element down low, and mostly the crew is focused on making sure the flight controls were giving the right inputs based on the TFR and attack radar displays. This was easy to interpret since the TFR would give different aural indications in our headsets based on commanding a climb or decent. So if the radar shadows were diverging then we were listening to make sure the aircraft was commanding a climb and conversely if the shadows were converging indicating we were over the terrain we were ok.
‘The beam width on the TFR radars was very narrow meaning flying down a canyon the wingtip clearance could be as small as 50 feet, which definitely made for some real excitement while the airplane is flying hands off.
‘But things really got exciting when we flew in clouds or at night over the terrain with TFR. Frequently, we were flying so close to the mountains that you could suddenly see flashes of our lights off the mountains as we flew in and out of clouds at night.
‘We were concentrating 100% on making sure the system wasn’t going to kill us, is certainly not an exaggeration.’
‘Flying this low is not for the faint of heart, but we did it day in and day out practicing to make sure we could fly under the enemy’s radar view.
Photo credit: U.S. Air Force