The modern, well-equipped multiengine airplane can be  remarkably capable under many circumstances. But, as  with single-engine airplanes, it must be flown prudently by  a current and competent pilot to achieve the highest possible  level of safety. This chapter contains information and guidance on the  performance of certain maneuvers and procedures in small  multiengine airplanes for the purposes of flight training  and pilot certification testing. The airplane manufacturer  is the final authority on the operation of a particular make  and model airplane. Flight instructors and students should  use the Federal Aviation Administration’s Approved Flight  Manual (AFM) and/or the Pilot’s Operating Handbook (POH)  but realize that the airplane manufacturer’s guidance and  procedures take precedence. The basic difference between operating a multiengine  airplane and a single-engine airplane is the potential problem  involving an engine failure. The penalties for loss of an engine  are twofold: performance and control. The most obvious  problem is the loss of 50 percent of power, which reduces  climb performance 80 to 90 percent, sometimes even more.  The other is the control problem caused by the remaining  thrust, which is now asymmetrical. Attention to both these  factors is crucial to safe OEI flight. The performance and  systems redundancy of a multiengine airplane is a safety  advantage only to a trained and proficient pilot. Pilots of single-engine airplanes are already familiar with many  performance “V” speeds and their definitions. Twin-engine  airplanes have several additional V-speeds unique to OEI  operation. These speeds are differentiated by the notation “SE”  for single engine. A review of some key V-speeds and several  new V-speeds unique to twin-engine airplanes are listed below. With regard to climb performance, the multiengine airplane,  particularly in the takeoff or landing configuration, may be  considered to be a single-engine airplane with its powerplant  divided into two units. There is nothing in 14 CFR part 23  that requires a multiengine airplane to maintain altitude while  in the takeoff or landing configuration with OEI. In fact,  Unless otherwise noted, when V-speeds are given in the  AFM/POH, they apply to sea level, standard day conditions  at maximum takeoff weight. Performance speeds vary with  aircraft weight, configuration, and atmospheric conditions.  The speeds may be stated in statute miles per hour (mph)  or knots (kt), and they may be given as calibrated airspeeds  (CAS) or indicated airspeeds (IAS). As a general rule, the  newer AFM/POHs show V-speeds in knots indicated airspeed  (KIAS). Some V-speeds are also stated in knots calibrated  airspeed (KCAS) to meet certain regulatory requirements.  Whenever available, pilots should operate the airplane from  published indicated airspeeds. Above the single-engine absolute ceiling, V$_{YSE}$ yields  the minimum rate of sink. General Terms and Definitions 12-2 • V$_{R}$—rotation speed—speed at which back pressure is  applied to rotate the airplane to a takeoff attitude. • V$_{LOF}$—lift-off speed—speed at which the airplane leaves  the surface. (NOTE: Some manufacturers reference  takeoff performance data to V$_{R}$, others to V$_{LOF}$.) • V$_{X}$—best angle of climb speed—speed at which the  airplane gains the greatest altitude for a given distance  of forward travel. • V$_{XSE}$—best angle-of-climb speed with OEI. • V$_{Y}$—best rate of climb speed—speed at which the  airplane gains the most altitude for a given unit of time. • V$_{YSE}$—best rate of climb speed with OEI. Marked  with a blue radial line on most airspeed indicators.  • V$_{SSE}$—safe, intentional OEI speed—originally known  as safe single-engine speed, now formally defined in  Title 14 of the Code of Federal Regulations (14 CFR)  part 23, Airworthiness Standards, and required to be  established and published in the AFM/POH. It is the  minimum speed to intentionally render the critical  engine inoperative. • V$_{REF}$—reference landing speed—an airspeed used  for final approach, which adjust the normal approach  speed for winds and gusty conditions. V$_{REF}$ is 1.3 times  the stall speed in the landing configuration. • V$_{MC}$—minimum control speed with the critical engine  inoperative—marked with a red radial line on most  airspeed indicators. The minimum speed at which  directional control can be maintained under a very  specific set of circumstances outlined in 14 CFR part  23, Airworthiness Standards. Under the small airplane  certification regulations currently in effect, the flight  test pilot must be able to (1) stop the turn that results  when the critical engine is suddenly made inoperative  within 20° of the original heading, using maximum  rudder deflection and a maximum of 5° bank, and  (2) thereafter, maintain straight flight with not more  than a 5° bank. There is no requirement in this  determination that the airplane be capable of climbing  at this airspeed. V$_{MC}$ only addresses directional  control. Further discussion of V$_{MC}$ as determined  during airplane certification and demonstrated in pilot  training follows in minimum control airspeed (V$_{MC}$)  demonstration.  [Figure 12-1]