V MC Demonstration Area XIV, Task E Revised 2015-08-13 Objective To learn how to recognize and recover from a loss of directional control caused by an asymmetrical thrust condition at low airspeed. Elements Attention-Getter Introduction / Motivation Theory Behind the V MC Demo Definitions Published V MC Speed Determining the Critical Engine Factors Affecting V MC Training Considerations V MC vs. V S Other Training Considerations Analyzing the Attention-Getter Scenarios Procedure for Performing V MC Demo Setting Up the Maneuver: Entry Altitude, Clearing Turns, Configuration Entering the Maneuver When to Recover Recovery Procedure Practicing V MC Demo in the Aircraft Schedule Times may vary based on pilot s ability. Preflight Briefing: 20 minutes Instructor Demonstration and Student Practice: 30 minutes (will be combined w/ other maneuvers in 2-hr training flight) Postflight Debriefing: 15 minutes References Airplane Flying Handbook (FAA-H-8083-3) Ch. 12 pg. 12-27 to 12-31 Flying Light Twins Safely (FAA-P-8740-66) Piper Seminole PA-44-180 Pilot s Operating Handbook, paragraph 4.47 (2000-model) / 4.51 (1979-model) ATP Piper Seminole Training Supplement Equipment Multi-Engine Aircraft: Piper Seminole PA-44 Whiteboard and marker OR paper and pencil Model aircraft (optional) 1 of 7
Common Student Errors Inadequate knowledge of the causes of loss of directional control at airspeeds less than V MC, factors affecting V MC, and safe recovery procedures. Improper entry procedures, including selecting too low of an entry altitude and using improper pitch, bank, or airspeed. Failure to configure the aircraft properly. Failure to maintain 5 of bank into the operating engine. Failure to recognize loss of directional control or indications of a stall. Failure to use the proper recovery procedure. Failure to clear the area before the maneuver. Excessive focus on cockpit instruments. Scenarios Scenario 1: You are on final approach to land after having lost the right engine during your flight. You re a bit low and slow, so you add power and raise the nose, but you aren t accelerating very much. The aircraft starts yawing to the right. What should you do? Scenario 2: You are in the clouds on an IFR flight, and you are climbing to meet a minimum crossing altitude. Your left engine has been running rough for the past several minutes, and you ve had to add more and more power on the right engine to keep climbing. The aircraft begins to yaw and roll to the left. What should you do? Completion Standards Before receiving an endorsement for their checkride, the student shall consistently execute the V MC Demonstration according to ATP s procedures while meeting or exceeding the Practical Test Standards. (See instructor notes for PTS.) This may require multiple instructional periods; the instructor shall ensure that adequate progress is made during each lesson. Instructor Notes Attention Getter https://www.youtube.com/watch?v=zr6ilrin234#t=28m09s to 29:35 (clip from FAA Safety Forum talk w/ animation) https://www.youtube.com/watch?v=2iinesxknzi#t=40s to end (ATSB animation) Introduction/Motivation Pilots transitioning from single-engine airplanes to multi-engine airplanes have some new things to consider and prepare for in the event they experience an engine failure in flight. An engine failure in a single-engine aircraft results in a 100% loss of power, leaving the pilot with no choice but to pitch for best glide and land somewhere within gliding range. However, if an engine fails in a multi-engine aircraft, there is still one engine operating. This is a great advantage when it comes to reaching a safe landing site; however, the asymmetrical thrust and lift negatively impact the controllability and handling characteristics of the airplane. The operating engine is offset from the center of gravity, causing the thrust to push the wing, leading to an uncommanded turn towards the dead engine. Pilots counteract this turn by applying rudder in the opposite direction. However, if the airspeed is slow, the reduction of airflow over the rudder reduces the rudder s effectiveness. At a certain airspeed, the asymmetrical thrust and lift will overpower the rudder s ability to resist the yawing and rolling motion. This airspeed is known as minimum controllable airspeed, or V MC. To counter these forces, the pilot must reduce power to eliminate asymmetric thrust, and reduce angle of attack to both reduce P-factor and increase the airspeed/airflow over the rudder. These actions will enable the pilot to maintain directional control of the airplane. The risk of an encounter with V MC is greatest during takeoff and initial climb, due to slow airspeeds, high power settings, and high angles of attack (where P-Factor is the most prominent). If a pilot experiences an engine failure immediately after takeoff, they will only have seconds to recover before the situation develops into a fatal accident. In order to prepare for this, we practice a maneuver call the V MC Demo. We will rehearse this maneuver in training over and over to develop the ability to recognize and recover from a loss of directional control. Our goal as instructors is to ensure that our students have the muscle memory and hand-eye coordination necessary to recover from a V MC scenario. 2 of 7
Theory 1. Definitions A. V MC : minimum control speed with the critical engine inoperative (14 CFR 1.2); the calibrated airspeed at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the airplane with that engine still inoperative, and thereafter maintain straight flight at the same speed with an angle of bank of not more than 5 degrees (14 CFR 23.149(a)). B. Critical engine: the engine whose failure would most adversely affect the performance or handling qualities of an aircraft (14 CFR 1.1) C. Directional control: Directional control has been lost when the pilot is applying full rudder deflecting into the operating engine, and the aircraft is yawing towards the inoperative engine. 2. Published V MC Speed A. AFM/POH includes a published V MC determined during certification, but this was determined under a very specific set of conditions (listed in 14 CFR 23.149 more on these later) B. Published V MC in the PA-44 Seminole is 56 KIAS much slower than we usually fly (unless practicing slow flight) so we sometimes don t pay as much attention to it as we should i. This can lead to bad habits when moving to higher-performance twins. E.g. Beech Baron (G58) V MC is 84 KIAS, V R is 85 KIAS, V X is 92 KIAS. Much smaller margins, need to react promptly to engine failure to avoid loss of control. 3. Determining the Critical Engine A. For conventional twins (both props spinning clockwise when viewed from behind), V MC is higher when the left engine fails than the right left engine is critical engine. B. Four reasons why, use mnemonic PAST i. P-Factor when aircraft is at a higher angle of attack, descending prop blade on right side of engine makes more thrust; right blade of right engine is further from CG, causing stronger yawing effect ii. Accelerated slipstream right side of prop creates more slipstream over the wing and hence more lift; extra lift acts further from the CG on the right wing, causing stronger rolling effect iii. Spiraling slipstream rotating air from left engine pushes on left side of vertical stabilizer and yaws aircraft to the left, offsetting tendency to turn right following right engine failure. No such effect from right engine, air spirals away from airplane. iv. Torque props rotate to the right, so by Newton s Third Law, plane wants to roll left. Adds to rolling tendency if left engine fails, offsets rolling tendency if right engine fails. C. Piper Seminole has counter-rotating props, therefore no critical engine. 4. Factors Affecting V MC A. Best way to look at these consider the conditions used to determine V MC during certification, then ask how V MC is affected if those conditions change B. V MC certification rules are found in 14 CFR 23.149 C. Use mnemonic SMACFUM (SMACFUM isn t in the regulation it s just a convenient way to remember the factors. 14 CFR 23.149 is the official wording, not SMACFUM.) i. Sea level, standard day Density altitude equals zero, basically. If density altitude increases, engines generate less thrust, easier for control surfaces to overcome asymmetric thrust. V MC decreases with increasing altitude. ii. Most unfavorable weight Lighter airplane has less lift, so tilting lift vector sideways (i.e. banking aircraft) to offset turning tendency is less effective. V MC decreases with increasing weight. iii. Aft center of gravity Shortens the arm through which the rudder force acts, makes rudder less effective. (Think about closing a door by pushing near the hinge vs. near the handle.) V MC decreases with forward CG. iv. Critical engine windmilling Critical engine was already discussed. Windmilling prop creates much more drag than feathered prop, creates stronger yawing tendency. V MC decreases when prop is feathered. v. Flaps/trim/cowl flaps for takeoff, gear up Lowered gear and gear doors add a keel effect that stabilizes airplane. Other items: V MC situation is most likely to occur just after takeoff (high power setting, relatively low airspeed). (Common error to avoid many students say flaps up, but it s actually flaps set for takeoff ) vi. Up to 5 bank Adding bank offsets turning tendency and maintains controllability, but also reduces performance. FAA decided 5 is reasonable compromise. V MC decreases with increasing bank (roughly 3 knots per degree). Implication if engine quits while in wings-level flight, V MC is up to 15 kts faster until pilot banks into the good engine. 3 of 7
1. 5 isn t necessarily the angle for zero sideslip. Zero sideslip is a performance consideration to help hold altitude. 5 bank is a controllability consideration to help hold a heading. vii. Max power on operating engine Creates maximum amount of asymmetric thrust. Note that part of recovery procedure in V MC Demo is reducing power on working engine until control is regained. V MC decreases with lower power setting. D. We aren t test pilots we don t know exactly how much a particular change in one of these factors will increase/ decrease V MC. Knowing the published V MC doesn t mean you know the actual V MC right now. Can t ignore V MC just because we re faster than 56 knots. Must be ready to recognize/recover from loss of directional control whenever operating at low airspeeds. 5. Training Considerations V MC vs. V S A. We ve discussed inadvertent V MC encounters in the real world what about the deliberate demonstration of V MC in the training environment? i. V MC Demo is safe if done correctly that said, it does involve deliberately approaching an uncontrolled condition while in a low-energy state. So we need to be careful. B. One consideration: relationship between V MC and stall speed i. V MC decreases with increasing density altitude, but V S does not. ii. Above some altitude, you can t actually reach V MC without stalling first called the critical altitude iii. Important consideration for training purposes because we need to be high enough to conduct the maneuver safely, therefore we are more likely to be at or above the critical altitude. C. Exact altitude depends on several factors: i. Weather conditions changes in temperature, pressure, and humidity change the density altitude ii. Aircraft loading higher weight and/or forward CG increases V S and decreases V MC, so the critical altitude is lower iii. Too many variables to calculate the exact altitude, so we always need to be aware that we may see stall indication before loss of directional control. Or if we re right at the critical altitude, may see both at the same time. D. Stalling a multi-engine aircraft while under asymmetrical power is a very bad idea. i. Stall plus yaw equals a spin entry. ii. Twins do not have to demonstrate spin recovery during certification. iii. Twins generally have very poor spin recovery characteristics. E. This is why we execute a recovery at any indication of an impending stall stall warning horn, buffeting, rapid decay in control effectiveness as well as at the loss of directional control. Must not stall the airplane during V MC Demo. F. The Piper Seminole is one of the few twins out there where the published V MC is less than the published V S you will usually reach a stall indication before losing directional control (but don t assume you will). i. To demonstrate actual loss of directional control, artificially raise V MC by limiting rudder travel ( rudder block ) or not using bank angle. 6. Other Training Considerations A. Appropriate altitude at least 4,000 AGL i. V MC has nothing to do with maintaining altitude definition refers to straight flight, not straight and level flight ii. We must reduce the angle of attack and the power setting during the recovery will cause us to lose altitude iii. If we mess up the maneuver and lose control of the aircraft, we want plenty of room to recover. iv. Conclusion: 4,000 AGL may be higher than required for most maneuvers, but we do need the extra space below us B. Performing the maneuver slowly i. The word slowly shows up about 4 times in the procedure for this maneuver. It s important. ii. V MC must be approached gradually. Slow down too quickly and you might blow right past V MC and lose control of the aircraft. iii. Reintroduce power slowly to make sure you have regained directional control before applying full power. C. Configuration meant to imitate V MC certification rules where possible i. Sea level/standard day can t do that, we need a safe altitude, and the weather is out of our control 4 of 7
ii. Most unfavorable weight and Aft CG can t do that, we need 2 people in the front seats, and we start the flight with full fuel for safety iii. Everything else critical engine windmilling, flaps for takeoff and gear up, up to 5 of bank, and max power on operating engine is part of the V MC Demo procedure 7. Analyzing the Attention-Getter Scenarios A. Let s use what we learned about V MC to analyze the video clips from the beginning of the lesson B. First animation (from the FAA Safety Forum) i. Watch the airspeed indicator and note the red radial line marking V MC. ii. Pilot lifts off about 5 knots below V MC. iii. Right engine fails immediately after liftoff with insufficient airspeed, pilot has no chance of maintaining control. 1. Only possible way to survive would be to close the left throttle, but it s nearly impossible to react fast enough iv. Lesson don t rotate before V MC. C. Second animation (from the ATSB, Australia s accident investigation board) [Note this example/explanation is more advanced. Include only if student has a good grasp of V MC concepts.] i. Left seat pilot was doing an instrument proficiency check with a training captain / check airman in the right seat. Part of check was a simulated engine failure on takeoff. ii. Embraer EMB-120 (like most twin-turboprop regional airliners) has an autofeather system prop automatically feathers if engine fails on takeoff, pilot doesn t have to take action. Certification rules for transport category aircraft say that if you have autofeather, V MC is calculated with the prop feathered. iii. Check pilot was supposed to reduce power lever to zero thrust to simulate a failed engine with a feathered prop like how we use 12 of manifold pressure to simulate feather on single-engine approaches in the Seminole. iv. Instead, check pilot pulled power lever all the way back to idle. Prop was windmilling much more drag than when feathered, increasing V MC above the published figure. v. Crew does not respond properly 1. Watch attitude indicator pilot doesn t establish 5 bank into good engine 2. Watch airspeed indicator pilot lets the airplane slow down 3. Watch right engine torque pilot adds more power on the good engine 4. Watch left engine torque check pilot never terminates the maneuver even when it s clear things have gone wrong Procedure 1. Select an altitude at or above 4,000 AGL. 2. Conduct clearing turns to the left and right. 3. Configure the aircraft in the clean configuration A. Gear up, flaps up (takeoff flap setting) B. Mixtures rich, props forward C. Fuel pumps on 4. Slowly close left throttle while maintaining heading and altitude. 5. Slow to approximately 10 knots above V YSE 100 KIAS. 6. Slowly increase right throttle (operating engine) to full power. Use rudder to maintain directional control and bank up to 5 towards the operating engine. 7. Increase pitch attitude slowly, decrease airspeed at approximately 1 knot per second until full rudder is applied to maintain directional control. 8. Recover at first sign of: A. Loss of directional control, OR B. First indication of a stall (stall horn or buffet) 9. Recover promptly by simultaneously reducing power sufficiently on the operating engine while decreasing the angle of attack as necessary to regain directional control within 20 of entry heading. 5 of 7
10. Continue recovery by increasing power slowly on operating engine while maintaining an angle of attack that allows for airspeed to increase to a point where directional control can be maintained with a minimum loss of altitude. 11. Accelerate to V XSE /V YSE 82-88 KIAS. 12. Bring throttles slowly together to 20 manifold pressure. 13. Execute the cruise checklist. Commercial AMEL PTS (FAA-S-8081-12C), Area of Operation X, Task B: 1. Exhibits satisfactory knowledge of the elements related to V MC by explaining the causes of loss of directional control at airspeeds less than V MC, the factors affecting V MC, and safe recovery procedures. 2. Configures the airplane in accordance with the manufacturer s recommendation, in the absence of the manufacturer s recommendations, then at V SSE /V YSE, as appropriate A. Landing gear retracted. B. Flaps set for takeoff. C. Cowl flaps set for takeoff. D. Trim set for takeoff. E. Propellers set for high RPM. F. Power on critical engine reduced to idle. G. Power on operating engine set to takeoff or maximum available power. 3. Establishes a single-engine climb attitude with the airspeed at approximately 10 knots above V SSE or V YSE, as appropriate. 4. Establishes a bank toward the operating engine, as required for best performance and controllability. 5. Increases the pitch attitude slowly to reduce the airspeed at approximately 1 knot per second while applying rudder pressure to maintain directional control until full rudder is applied. 6. Recognizes indications of loss of directional control, stall warning, or buffet. 7. Recovers promptly by simultaneously reducing power sufficiently on the operating engine while decreasing the angle of attack as necessary to regain airspeed and directional control. Recovery should not be attempted by increasing the power on the simulated failed engine. 8. Recovers within 20 of the entry heading. 9. Advances power smoothly on operating engine and accelerates to V XSE /V YSE, as appropriate, ±5 knots, during the recovery. A. Private pilot applicants are allowed +10/-5 knots on the airspeed tolerance. 6 of 7
Images (from Airplane Flying Handbook) Forces created during single-engine operation. Effect of CG location on yaw. Graph depicting relationship of V MC to V S. 7 of 7