The Blackbird
No reconnaissance plane has ever flown through more dangerous skies—or with greater freedom from interference—than the SR-71 Blackbird. It holds the record as the fastest aircraft powered by air‑breathing engines, and its capabilities and mission successes made it the crowning achievement of aviation technology during the Cold War.
The U.S. Air Force retired all SR-71 aircraft on January 26, 1990, due to shrinking defense budgets and the jet’s high operating costs.
Over its almost 24 years in service, the SR-71 kept its status as the world’s highest‑flying and fastest operational aircraft. From an altitude of 80,000 feet, it was able to observe as much as 100,000 square miles of the Earth’s surface every hour.
Blackbird Top Speed
Today, there is a lot of speculation about the SR-71’s true top speed. In reality, the maximum speed was restricted by the temperature limits of its J58 engines. Ironically, the airframe itself wasn’t the limiting factor—the engines were. Just ahead of the engine’s compressor sat a temperature sensor that displayed readings to the pilot; once it reached about 427°C (800°F), the aircraft had reached its permitted speed limit.
However, as Paul Crickmore explains in his new book, Lockheed Blackbird: Beyond the Secret Missions – The Missing Chapters, the SR-71 was able to fly faster during bomb damage assessment missions over Libya in support of Operation El Dorado Canyon in April 1986 because the 427°C temperature limit was lifted.
SR-71 BDA Flights
As mentioned earlier, SR-71 pilots normally had to stay below an inlet temperature of 427°C, which was the standard maximum. This limit existed because the compressor inlets determined how fast the jet could safely fly. For Operation El Dorado Canyon, however, a WARTIME EMERGENCY limit was introduced, raising the maximum temperature from 427°C to 450°C.
This meant that, for the sake of mission success, crews were allowed to fly the aircraft faster than usual. Afterward, the first-stage compressor had to be thoroughly inspected so mechanics could check the engines for any damage.
Flight testing has shown that at Mach 3.4, unstable airflow in the SR-71’s inlet reaches the engine and can cause a flameout—and indeed, the SR-71 experienced several flameouts over its career.
As previously noted, SR-71 pilot Brian Shul said he reached Mach 3.5 during a bomb damage assessment mission in support of Operation El Dorado Canyon. Based on the information presented in Paul Crickmore’s new book, that speed was entirely achievable with the inlet maximum temperature raised to 450°C.
SR-71 Blackbird final flight
In addition, during SR-71 #972’s record flight from California to Virginia, a Skunk Works engineer suggested lifting the 427°C temperature limit for that final trip. The engines might have been damaged, but since it was the aircraft’s last flight, that was considered acceptable. The U.S. Air Force declined, however, because they did not want to highlight that they were removing the SR-71 Blackbird—with its remarkable range and speed—from service.
Noteworthy, for the final flight a speed run could’ve been done in less than 68 minutes. Butch Sheffield, who was working for the Skunk Works Washington DC division, was in charge of the final flight.
It’s worth noting that, on this last flight, the speed run could have been completed in under 68 minutes. The mission was overseen by Butch Sheffield of the Skunk Works Washington, D.C. office.
Check out Habubrats SR-71 and Born into the Wild Blue Yonder Facebook pages for further Blackbird photos and stories.
Photos by U.S. Air Force
