MULTIENGINE FLIGHT GENERAL - FAASafety.gov

1 MULTIENGINE FLIGHTThis chapter is devoted to the factors associated withthe operation of small MULTIENGINE airplanes. For thepurpose of this handbook, a small MULTIENGINE air-plane is a reciprocating or turbopropeller-poweredairplane with a maximum certificated takeoff weightof 12,500 pounds or less. This discussion assumes aconventional design with two engines one mountedon each wing. Reciprocating engines are assumedunless otherwise noted. The term light-twin, although not formally defined in the regulations, isused herein as a small MULTIENGINE airplane with amaximum certificated takeoff weight of 6,000 poundsor are several unique characteristics of multiengineairplanes that make them worthy of a separate class rat-ing. Knowledge of these factors and proficient flightskills are a key to safe FLIGHT in these airplanes. Thischapter deals extensively with the numerous aspects ofone engine inoperative (OEI) FLIGHT .

2 However, pilotsare strongly cautioned not to place undue emphasison mastery of OEI FLIGHT as the sole key to flyingmultiengine airplanes safely. The inoperative engineinformation that follows is extensive only becausethis chapter emphasizes the differences between flyingmultiengine airplanes as contrasted to modern, well-equipped MULTIENGINE airplane canbe remarkably capable under many circumstances. But,as with single-engine airplanes, it must be flown pru-dently by a current and competent pilot to achieve thehighest possible level of chapter contains information and guidance on theperformance of certain maneuvers and procedures insmall MULTIENGINE airplanes for the purposes of flighttraining and pilot certification testing. The finalauthority on the operation of a particular make andmodel airplane, however, is the airplane the FLIGHT instructor and the student should beaware that if any of the guidance in this handbook con-flicts with the airplane manufacturer s recommendedprocedures and guidance as contained in the FAA-approved Airplane FLIGHT Manual and/or Pilot sOperating Handbook (AFM/POH), it is the airplanemanufacturer s guidance and procedures that basic difference between operating a multiengineairplane and a single-engine airplane is the potentialproblem involving an engine failure.

3 The penalties forloss of an engine are twofold: performance and most obvious problem is the loss of 50 percentof power, which reduces climb performance 80 to 90percent, sometimes even more. The other is the con-trol problem caused by the remaining thrust, whichis now asymmetrical. Attention to both these factorsis crucial to safe OEI FLIGHT . The performance andsystems redundancy of a MULTIENGINE airplane is asafety advantage only to a trained and AND DEFINITIONSP ilots of single-engine airplanes are already familiarwith many performance V speeds and their defini-tions. Twin-engine airplanes have several additionalVspeeds unique to OEI operation. These speeds aredifferentiated by the notation SE , for single review of some key V speeds and several new Vspeeds unique to twin-engine airplanes follows. VR Rotation speed. The speed at which backpressure is applied to rotate the airplane to a take-off attitude.

4 VLOF Lift-off speed. The speed at which theairplane leaves the surface. (Note: some manu-facturers reference takeoff performance data toVR, others to VLOF.) VX Best angle of climb speed. The speed atwhich the airplane will gain the greatest altitudefor a given distance of forward travel. VXSE Best angle-of-climb speed with oneengine inoperative. VY Best rate of climb speed. The speed atwhich the airplane will gain the most altitude fora given unit of time. VYSE Best rate-of-climb speed with one engineinoperative. Marked with a blue radial line onmost airspeed indicators. Above the single-engineabsolute ceiling, VYSE yields the minimum rate ofsink. VSSE Safe, intentional one-engine-inoperativespeed. Originally known as safe single-engine12-1Ch 5/7/04 9:54 AM Page 12-1speed. Now formally defined in Title 14 of theCode of Federal Regulations (14 CFR) part 23,Airworthiness Standards, and required to beestablished and published in the AFM/POH.

5 It isthe minimum speed to intentionally render thecritical engine inoperative. VMC Minimum control speed with the criticalengine inoperative. Marked with a red radial lineon most airspeed indicators. The minimum speedat which directional control can be maintainedunder a very specific set of circumstances outlinedin 14 CFR part 23, Airworthiness the small airplane certification regulationscurrently in effect, the FLIGHT test pilot must be ableto (1) stop the turn that results when the criticalengine is suddenly made inoperative within 20 of the original heading, using maximum rudderdeflection and a maximum of 5 bank, and (2)thereafter, maintain straight FLIGHT with notmore than a 5 bank. There is no requirement inthis determination that the airplane be capableof climbing at this airspeed. VMConlyaddresses directional control. Further discus-sion of VMCas determined during airplane cer-tification and demonstrated in pilot trainingfollows in minimum control airspeed (VMC)demonstration.

6 [Figure 12-1]Figure 12-1. Airspeed indicator markings for a otherwise noted, when V speeds are given inthe AFM/POH, they apply to sea level, standard dayconditions at maximum takeoff weight. Performancespeeds vary with aircraft weight, configuration, andatmospheric conditions. The speeds may be stated instatute miles per hour ( ) or knots (kts), and theymay be given as calibrated airspeeds (CAS) or indi-cated airspeeds (IAS). As a GENERAL rule, the newerAFM/POHs show V speeds in knots indicated airspeed(KIAS). Some V speeds are also stated in knots cali-brated airspeed (KCAS) to meet certain regulatoryrequirements. Whenever available, pilots should oper-ate the airplane from published indicated regard to climb performance, the multiengineairplane, particularly in the takeoff or landing con-figuration, may be considered to be a single-engineairplane with its powerplant divided into two is nothing in 14 CFR part 23 that requires amultiengine airplane to maintain altitude while inthe takeoff or landing configuration with one engineinoperative.

7 In fact, many twins are not required todo this in any configuration, even at sea current 14 CFR part 23 single-engine climbperformance requirements for reciprocating engine-powered MULTIENGINE airplanes are as follows. More than 6,000 pounds maximum weightand/or VSOmore than 61 knots: the single-engine rate of climb in feet per minute ( ) at5,000 feet MSL must be equal to at least .027 VSO2. For airplanes type certificated February 4,1991, or thereafter, the climb requirement isexpressed in terms of a climb gradient, per-cent. The climb gradient is not a direct equiva-lent of the .027 VSO2formula. Do not confuse thedate of type certification with the airplane smodel year. The type certification basis of manymultiengine airplanes dates back to CAR 3 (theCivil Aviation Regulations, forerunner of today sCode of Federal Regulations). 6,000 pounds or less maximum weight and VSO61 knots or less: the single-engine rate of climbat 5,000 feet MSL must simply be rate of climb could be a negative is no requirement for a single-enginepositive rate of climb at 5,000 feet or any otheraltitude.

8 For light-twins type certificatedFebruary 4, 1991, or thereafter, the single-engine climb gradient (positive or negative) issimply of climb is the altitude gain per unit of time, whileclimb gradient is the actual measure of altitude gainedper 100 feet of horizontal travel, expressed as a per-centage. An altitude gain of feet per 100 feet oftravel (or 15 feet per 1,000, or 150 feet per 10,000) is aclimb gradient of is a dramatic performance loss associated withthe loss of an engine, particularly just after airplane s climb performance is a function ofthrust horsepower which is in excess of that required12-2Ch 5/7/04 9:54 AM Page 12-2for level FLIGHT . In a hypothetical twin with each engineproducing 200 thrust horsepower, assume that the totallevel- FLIGHT thrust horsepower required is 175. In thissituation, the airplane would ordinarily have a reserveof 225 thrust horsepower available for climb.

9 Loss ofone engine would leave only 25 (200 minus 175) thrusthorsepower available for climb, a drastic level rate-of-climb performance losses of at least80 to 90 percent, even under ideal circumstances, aretypical for MULTIENGINE airplanes in OEI OF SYSTEMSThis section will deal with systems that are generallyfound on MULTIENGINE airplanes. MULTIENGINE airplanesshare many features with complex single-engine air-planes. There are certain systems and features coveredhere, however, that are generally unique to airplaneswith two or more propellers of the MULTIENGINE airplane may out-wardly appear to be identical in operation to theconstant-speed propellers of many single-engineairplanes, but this is not the case. The propellers ofmultiengine airplanes are featherable, to minimizedrag in the event of an engine failure. Dependingupon single-engine performance, this feature oftenpermits continued FLIGHT to a suitable airport followingan engine failure.

10 To feather a propeller is to stopengine rotation with the propeller blades streamlinedwith the airplane s relative wind, thus to minimizedrag. [Figure 12-2]Feathering is necessary because of the change in para-site drag with propeller blade angle. [Figure 12-3]When the propeller blade angle is in the featheredposition, the change in parasite drag is at a minimumand, in the case of a typical MULTIENGINE airplane, theadded parasite drag from a single feathered propelleris a relatively small contribution to the airplane the smaller blade angles near the flat pitch position,the drag added by the propeller is very large. At thesesmall blade angles, the propeller windmilling at can create such a tremendous amount of drag thatthe airplane may be uncontrollable. The propeller wind-milling at high speed in the low range of blade anglescan produce an increase in parasite drag which may beas great as the parasite drag of the basic a review, the constant-speed propellers on almostall single-engine airplanes are of the non-feathering,oil-pressure-to-increase- pitch design.