Air Minimum Control Speed—The Ever-Present Assassin

First, let me state that I am an old C-130 pilot, a biology major—and not an engineer of any kind. I retired from the USAF in 2011, but I am still hanging on to government employment as the senior C-130J Military Flight Operations Quality Assurance Analyst at Headquarters, Air Mobility Command. I was fortunate to fly four models of the C-130 during my USAF flying career. The order of flight was C-130E, C-130H, C-130E, C-130B, C-130E, and C-130J. My favorite aircraft was the B-model, but that is a story for another day.

I was trained to fly C-130s in 1975 by high-time Instructor Pilots at the Rock (Little Rock Air Force Base, AR), still fresh from their Vietnam flying experiences. They were outstanding pilots and mentors, full of good and bad flying habits learned the hard way during combat flying throughout Southeast Asia. All of them described what an extraordinarily strong and reliable aircraft the C-130 was. The advice that stuck with me for the rest of my flying career, however, was the four primary ways the aircraft could kill you, or you could kill yourself: propellers, bleed air, minimum control speed, and fin stall. Today’s C-130J pilots are fortunate that the “J†incorporates numerous safety measures. These safeguards include (1) a different, less mechanically complex propeller; (2) Advisory, Caution, and Warning Systems that warn us of impending stalls and sideslips; (3) right/left rudder instructions to bail us out of a fin stall; and (4) perhaps the most important of all—the Automatic Thrust Control System (ATCS) that will automatically assist the pilot in avoiding “below†minimum control speed issues following engine failure after takeoff. To counter the potentially deadly asymmetric power effects of much higher thrust-producing engines and propellers, the ATCS will automatically reduce power on the symmetrical engine following an engine failure, thereby lowering the minimum control speed to a more reasonable/achievable airspeed.

During my C-130J initial cadre training at the Lockheed Martin Corporation in early 2000, I took particular interest in the ATCS as explained by the Lockheed Martin instructors and engineers. We received detailed training on the much higher air minimum control airspeeds caused by greater engine/propeller thrust, with only minor changes in the flight control authority of the airframe design and control surfaces. I thought back to my Vietnam-era instructors and how much they would have appreciated an ATCS backing them up during those short runway, middle-of ­the-jungle takeoffs.

I recently read about a C-130H Class A Mishap where flying below air minimum control airspeed and turning into an inoperative engine were listed as factors in the mishap. I thought how great it would be if all C-130H model aircraft in the USAF inventory had ATCSs to protect them during the potentially catastrophic engine failure immediately after takeoff scenarios.

Hence the purpose of this article. I have recently discovered that some USAF C-130H aircraft are, or will be, modified with higher thrust-producing, eight-bladed propellers (NP2000)—adding a purported 20 percent greater thrust during low airspeed situations. In addition, some aircraft will receive the more efficient 3.5 engines along with the new propellers. These modifications apparently come without ATCS additions or changes in airframe design and/or flight control authority. Unless the heightened minimum control airspeed dangers are recognized by C-130H aircrews, along with receiving realistic simulator training on how to react to and safely fly out of an engine failure immediately after takeoff, there will be high risks ahead for some of our C-130H aircrews. The old “raise the dead and step on the ball†mnemonic might not be enough to counteract the increased asymmetric thrust unless safe airspeeds are achieved or symmetric engine thrust is correspondingly reduced. The safest way to achieve these goals is through realistic simulator training, and, if weapon system trainers are not available, very careful practice in the aircraft itself under strict instructor supervision.

In conclusion, my USAF C-130 flying career began at a time when C-130 aircraft malfunctions and system deficiencies caused nearly as many fatal mishaps as aircrew-induced mishaps. Newer model C-130s with systems and engineering improvements and built-in safeguards have virtually eliminated fatal aircraft malfunctions. My final message as retirement looms on the horizon, and 46 years of corporate C-130 memory departs the fix, is a warning for current C-130H and C-130J crewmembers. Always remain aware that when pushed out of its envelope, the “very capable†and forgiving C-130H/J can turn into a handful of uncontrollable terror and quickly end the lives of everyone on board. Therefore, be aware of and prepared for the low-airspeed engine failure immediately after takeoff, and recognize the serious threat associated with dropping below critical air minimum control speed during the recovery. The 60-plus-year flying history of the C-130 airframe is littered with below-minimum control speed-related fatalities, so how many more times will this lurking killer claim our crewmembers in the future? Do not let it happen to you!