Twin Proficiency: What’s This Vsse?

Twin Proficiency: What’s This Vsse?

VSSE: The safe, intentional one-engine inoperative speed. Originally known as “SafeSingle-Engine Speed.” Now formally defined in 14 CFR Part 23, Airworthiness Standards, and required to be established and published in the Approved Flight Manual/Pilot’s Operating Handbook. VSSE is the minimum speed to intentionally render the critical engine inoperative.

FAA Airplane Flying Handbook

Multi-engine airplanes have several significant advantages over single-airplane types. The advantage that is most, well, advantageous, is a matter of debate. Payload capability, center of gravity range, speed, and system redundancies are commonly cited as justifications for accepting the additional cost and complexity of owning and flying a piston twin, when compared to a high-performance piston single. The sole most common reason pilots choose a twin over a single, however, is the additional safety that comes with the second engine.

The irony is that if an engine fails in a single-engine airplane the aircraft tends to nose down and remain wings-level, remaining under control unless the pilot resists its natural tendencies. While when one engine in a conventional twin-engine airplane quits, the airplane will immediately, and sometimes dramatically, depart from controlled flight in all three axes (roll, pitch and yaw) unless the pilot actively prevents it from doing so. To actually benefit from the safety advantage of a multi-engine airplane, then, the pilot must actively and frequently practice engine-out scenarios under realistic conditions, while at the same time doing so in a safe and controlled environment.

The case can be made that preparing for an engine failure at a critical moment, such as immediately after takeoff, simply cannot be done safely in an actual airplane. Instead, it requires some sort of simulator-based training so the pilot can experience the “surprise factor,” and so both pilot and instructor can survive the inevitable mistakes that are part of the learning process.

For now, let’s look at one important factor in the simulation of engine failures in a piston twin in actual flight instruction. We’ve covered the other vital aspects of this training before (“Blue Line, White Arc, Red Radial”, T&T, October, 2012). There is another element of safe in-airplane engine failure presentation and practice, however, that many twin-engine pilots might not know (or remember), but which is critical to safety and, to the extent possible, vital for accurately presenting engine-out performance in training: VSSE. VSSE is defined at the beginning of this article. Operationally, VSSE is the slowest indicated airspeed at which an instructor should initiate the simulation of a failed engine in multiengine flight.

As an example, as I complete this article I’m about to go instruct a pilot in his Beechcraft Baron 58. Section X, the Safety Information portion of the Baron 58’s Pilot’s Operating Handbook (POH) expands upon the FAA’s definition to say:

VSSE is specified by the airplane manufacturer and is the minimum speed at which to perform intentional engine cuts. Use of VSSE is intended to reduce the accident potential from loss of control after engine cuts at or near minimum control speed (VMCA). VMCA demonstrations are necessary in training but should only be made at a safe altitude above the terrain and with power reduction on one engine made at or above VSSE.

The indicated speed for VSSE is published in the Emergency Procedures section of Baron POHs. The POH speeds do not vary much from one model to the next, as listed on this table:

Screen Shot 2016-03-07 at 8.39.00 AM

It’s very important to realize that VSSE is only five to six knots above single-engine loss of control speed (VMCA) in these airplanes! VSSE is far below single-engine best rate of climb speed (VYSE), which is your target airspeed immediately upon detecting an engine failure during takeoff or at the beginning of a balked landing/go-around. VSSE is about the liftoff speed for a Baron, which is usually five knots above the published calibrated VMCA.

Check your airplane’s POH and find your published VSSE. Compare that value to those for VMCA and VYSE to see how big (or small) the margin is between VSSE and the more commonly known single-engine speeds for the airplane you fly.

As a pilot, the importance of knowing VSSE is to recognize the crash history that resulted in a requirement to define VSSE in the first place, and to ensure that your multiengine instructor is experienced and familiar enough with the airplane you’re flying that he or she knows and adheres to the VSSE warning. In or out of training, consciously review, before every takeoff, that any engine anomaly, simulated or real, at a speed below VYSE requires an immediate pitch downward to increase airflow over the controls to make sure you can counteract the roll, yaw and pitch of asymmetric thrust, and thereby actually attain the safety benefits you sought when you chose to own and fly a twin-engine airplane.

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