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 Article 1

This article is presented as part o the 2007 Boeing Perormance and Flight Operations Engineering Conerence,providing continuing support or sae and ecient fight operations.

The Migration to HigherThrust Engines and the

Effect on Control Speeds

Status 

Steve NelsonBoeing Flight Operations Engineering

For the 777 airplane the growth in engine thrust levels has increased since theoriginal PW4074 engine. This original engine was rated at 74000 pounds o thrust and was envisioned to grow to around 95000 pounds o thrust. The 777-200LR hasa current oering o a 115000 pound thrust engine. With this engine growth the

 vertical tail and rudder size has remained the same. This has resulted in reducedmargins between the normal operating speed and the in-air minimum controlspeed

Yawing moment due

to aerodynamic controls

β

Large thrust

commanded from

operating engine

Yawing moment due

to thrust asymmetry

Failed engine

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2007 Performance and Flight Operations Engineering Conference

1.2

There is a speed below which there is a loss o directional control. This speed isdened by the inability to reliably maintain desired bank angle and/or heading at a given asymmetric thrust. This speed is always lower than the certied minimumcontrol speed (V 

MCA /V 

MCL).

FAR 25.149 states: “V MC

is the calibrated airspeed at which, when the critical engine

is suddenly made inoperative, it is possible to maintain control o the airplane withthat engine still inoperative and maintain straight fight with an angle o bank o not more than 5 degrees. Certied minimum operating speeds (V 

2, V 

REF) are always

at greater than or equal to V MCA 

, and hence, have even greater margin to the loss o directional control speed. All models o the 777 amily meet all minimum controlspeed regulations o all regulatory agencies where they are certied (FAA/EASA,etc). However, higher thrust asymmetry may cause the loss o directional controlspeed to become greater than stall warning speed at light weights. This raises thepossibility that i airspeed were improperly reduced below the published operating speeds at these weights and thrust levels, the limit o ull wheel and rudder controlinputs could be reached prior to stick shaker activation.

Flight crews ollowing Boeing published procedures and fying recommendedspeeds will maintain directional control. However, loss o directional control priorto reaching stick shaker may occur ater an engine ailure in combination with: light 

 weights, airspeeds lower than recommended, and higher than recommended thrust settings.

Landing Go-Around

One push o TO/GA button provides adequate thrust or most situations, andprovides substantial speed margin to loss o directional control speed in the event o an engine ailure. Two pushes o TO/GA button provides ull G/A thrust, reducing margin to loss o control speed in the event o an engine ailure.

 S t i c k   s h a

 k  e r

 VMCA 

Airspeed

Weight

Loss of directional control speed (higher thrust)

Loss of directional control speed (lower thrust)

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Steve Nelson | The Migration to Higher Thrust Engines and the Effect on Control Speeds

1.3

Analysis for Probability of Violating Minimum Control Speed:

Assumptions are as ollows:

• Engine ailure is very rare• Engine ailure during critical takeo phase (V 

1to V 

2+ 15) is very rare

• Engine ailure during go-around prior to acceleration is very rare

• With a xed derate takeo with an engine ailure the pilot advances thethrottle on the remaining engine to ull thrust (against Boeing publishedprocedures)

Conclusions are:

 When making conservative assumptions all cases are extremely improbable(and at light weights)

The Takeoff Case:

FULL-RATED or ASSUMED TEMPERATURE METHOD (ATM) Takeo:Full-rated takeo V 

2provides substantial speed margin to V 

MCA and loss o directional

control speed. Assumed Temperature Method (ATM) provides same or greater

margin, even i thrust is pushed (no reduction in V MC speeds assumed).

FIXED DERATE Takeo:Fixed derate takeo limit thrust in takeo calculations (VMC speeds are set by de-rated thrust level), yielding lower takeo speeds and shorter eld lengths. Pushing thrust higher upon engine ailure violates procedures and reduces or eliminatesmargin to V 

MCGand V 

MCA , and reduces margin to loss o directional control speed

Thrust levers should not be advanced beyond the xed derate limit unless one o theollowing conditions apply:

1) Conditions are encountered during the takeo where additional thrust isneeded on both engines such as windshear.

2) Thrust increase ollowing an engine ailure, especially near V1, could result in a loss o directional control, and should not be accomplished unless in theopinion o the Captain, terrain contact is imminent.

Flying Boeing procedures and recommended speeds will maintain directionalcontrol.

Loss of directional control speed

 L a r g e  f i x e d 

 d e r a t e  m i n i m

 u m  V 2

Airspeed

Weight

 S t i c k   s h

 a k  e r

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2007 Performance and Flight Operations Engineering Conference

1.4

Not ollowing Boeing procedures and advancing thrust reduces the margin to loss o directional control speed.

A V 2

foor is one o the technical solutions that we are looking at. The V 2

foor wouldmaintain the larger speed margin to the loss o directional control speed that is oundon the lower thrust engines.

LANDING GO-AROUND:

I an engine ails during a go-around, an immediate loss o airspeed will occur. It is important that airspeed loss be recovered. Airspeed recovery is accomplished by ollowing fight director guidance and Boeing recommended procedures.

One push o TO/GA button provides adequate thrust or most situations, andprovides substantial speed margin to loss o directional control speed in the event o 

an engine ailure.

Two pushes o TO/GA button provides ull G/A thrust, reducing margin to loss o control speed in the event o an engine ailure.

 Note: the minimum recommended approach speed is V REF

+ 5 knots.

The 777-200LR maintains an excellent margin to loss o control speed due to a V REF

 speed foor.

Boeing is currently evaluating speed margins or the 777-200ER at light weights tomatch 777-200LR methodology.

Loss of directional control speed

 L a r g e  f i x

 e d  d e r a t e

  m i n i m u m

   V 2

Airspeed

Weight

 S t i c k  

 s h a k  e r

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Steve Nelson | The Migration to Higher Thrust Engines and the Effect on Control Speeds

1.5

The Final Effect is of minimal impact (but not zero):

Minor model EngineExposure

(loss of control speed > stick shaker speed)

777-300/-300ER ALL NONE

777-200/-200ER

PW4074, 4077, 4084

RR 877, 884

GE90-76B, -85B

NONE

777-200ER

PW4090

RR 892

GE90-90B

Landing weights below ~365000 lb

777-200ERRR 895

GE90-94B

Takeoff weights below ~380000 lb

Landing weights below ~400000 lb

777-200LR

777 Freighter

GE90-110B1L

(GE90-115BL)

Takeoff weights below ~445000 lb

(Takeoff weights below ~465000 lb)

The Plan from Here:

Boeing will revise the 777 Flight Crew Training Manual in October 2007. Thisrevision will urther clariy and emphasize the importance o ollowing recommendedcrew procedures and maintaining adequate speed margins. Boeing will also publisha Flight Operations Review and an  Aero Magazine article to provide additional

 background and clariying inormation. Along with this emphasis on adhering toprocedures we are also looking at technical solutions.

Loss of directional control speed

 S t a l l - b a s e 

 V R E F

 VREF (floored)

Airspeed

Weight

 S t i c k   s h a k 

 e r