3. B767 Max Gross Takeoff Weight Problem

EXAM III REVIEW

Three Subunits

1.  Takeoff Fundamentals

2.  FAR Part 25

3.  B767 Max Gross Takeoff Weight Problem

Two Exam Parts

·  One (15 Questions): covers 1 & 2 above ONLY

·  Two (18 Questions): covers 1, 2, & 3 above

·  33 questions almost equally divided among 1, 2, & 3, with a slight emphasis on 2.

Format

·  All questions are objective (multiple choice or T/F)

·  Write on test booklet but answer on Scantron Form

·  Do NOT have to show work for calculations—but suggest you do show work on exam booklet

·  B767 lookup problems involve a single chart or table only—given the input, you must produce the required output

TAKEOFF FUNDAMENTALS

Liftoff (Ground) Speed / Takeoff Roll / Takeoff Time
Gross Weight:
W1 ® W2 / V2 = V1 Ö (W2 / W1) / X2 = X1 (W2 / W1)2 / t2 = t1 (W2 / W1)1.5
Density Ratio:
s1 ® s2 / V2 = V1 Ö (s1 / s2) / X2 = X1 (s1 / s2)2 / t2 = t1 (s1 / s2) 1.5
Temperature:
TA1 ® TA2 / V2 = V1 Ö (TA2 / TA1) / X2 = X1 (TA2 / TA1)2 / t2 = t1 (TA2 / TA1) 1.5
Headwind:
VW / V2 = V1 – VW / X2 = X1 (1 - VW / V1)2 / t2 = t1 (1 - VW / V1)
R/W Grad: RG &
T-W Ratio: RT/W / V2 = V1 / X2 = X1 [RT/W / (RT/W – RG)] / t2 = t1 [RT/W / (RT/W – RG)]

Rules of Thumb Deriving from these Equations

·  Example 1: A 21% increase in gross weight results in a 10% increase in liftoff speed.

§  W2 = 1.21 W1

§  V2 = V1 Ö (W2 / W1) = V1 Ö (1.21 W1 / W1) = V1 Ö1.21 = 1.1 V1

·  Example 2: A 10% increase in gross weight gives a 21% increase in takeoff distance

§  W2 = 1.1 W1

§  X2 = X1 (W2 / W1)2 = X1 (1.1W1 / W1)2 = X1 (1.1)2 = 1.21 X1

Graphical Approach to Wind Effect on Takeoff Ground Roll

Navy RF8 Crusader Takeoff Distance Chart (Guaranteed Problem)

Takeoff Acceleration Check

FAR Part 25: Air Transport Takeoff with Critical Engine Out

Definitions (where applicable, know why as well as what)

·  Critical Engine

·  Climb Gradient

·  Adequate Climb Capability (have climb gradients on study sheet!!!)

·  VXSE

·  VYSE

·  VMCG

·  VMCA

o  VMCG < VMCA

·  VMU

·  Vmu

o  VMU < Vmu—more vertical thrust at VMU, lower VLOF

·  V1

·  VR.

·  V2

Takeoff Speed Constraints for Airplane Certification

V1 Constraint / Rationale
V1 ≤ VR / No T/O rejection with nose wheel off the ground
V1 ≥ VMCG / Maintain directional control with nose wheel on ground
35’ AGL & V2 by runway end / Speed and altitude safety margins by end of runway
Low enough for safe stopping / Ability to reject takeoff without runway overrun
VR Constraint / Rationale
VR ≥ 1.10 VMU / Avoid getting airborne at high a and high DI (VMU < Vmu)
VR ≥ 1.05 Vmu / Avoid getting airborne at high a and high DI (Vmu > VMU)
VR ≥ 1.05 VMCA / Maintain directional control with nose wheel off ground
VR ≥ V1 / No T/O rejection with nose wheel off the ground
V2 Constraint / Rationale
High enough for safe climb / Meet required Part 25 V2 climb capability requirements
V2 ≥ 1.2 VS / Stall speed safety margin in T/O configuration
V2 ≥ 1.1 VMCA / Directional control safety margin during climb out

Note: V2 is a “compromise” speed:

·  Low enough achieve 35’ /V2 with engine failure at V1 and continued T/O.

·  High enough to allow “adequate climb capability.”

·  V2 < VXSE, which is speed for max climb angle with critical engine out.

Part 25 Takeoff Segments (critical engine fails at V1 and T/O continues)

Balanced Field Length—critical engine fails at V1

·  Accelerate-go Distance

·  Accelerate-stop Distance

·  Balanced Field Length

·  Balanced Field V1

Changing V1 from Balanced Field V1 Always Increases R/W Required for T/O

Runway

·  Slippery Runway—runway conditions that increase stop distance without affecting go-distance

·  Cluttered Runway—runway conditions that increase go distance without affecting stop distance.

Effect of Changes in Weight, Density Altitude, Slope, Runway Contamination on Balanced Field Length and Balanced Field V1

Dry Runway Distances

Note:

·  Increases in weight or density altitude, an upslope, or a cluttered runway necessitate an increase in BFL and BF V1.

·  However, a slippery, uncluttered runway at fixed weight and density altitude necessitates an increase in BFL but a reduction in BF V1 because of reduced braking effectiveness.

Stopway

·  a paved, weight-bearing, obstruction-free runway extension at least as wide as the runway itself.

·  Use all of a stopway to increase accelerate-stop distance

·  Results in an unbalanced field (stop distance > go distance)

Clearway

·  a clear area immediately off the end of the runway with no obstructions other than threshold lights 26” high or less, gradient no greater than 1.25%, and width at least 250’ on each side of the runway centerline.

·  Use ½ of a clearway to increase accelerate go distance

·  Results in an unbalanced field (go distance > stop distance)

Takeoff Distance Definitions

·  All definitions are for ambient conditions; i.e., varying conditions lead to varying distances.

·  All-Engine Takeoff Distance—the distance from the start of takeoff roll to V2 and 35’ AGL with all engines operating.

·  All-Engine Takeoff Field Length—115% of all-engine takeoff distance.

·  FAR Takeoff Field Length—the larger of

1.  Balanced Field Length; or

2.  All-Engine Takeoff Field Length.

·  Runway must be no shorter than FAR Takeoff Field Length.

Boeing 767 Max Gross Takeoff Weight Problem

·  Impossible to review thoroughly in a one hour session. Use online review notes and Q9 worksheets.

·  No sequential problems such as on Quiz 9: Exam lookup problems involve input and output from one chart only.

·  If you know the what and why of the Quiz 9 group report and know how to use the charts and tables, you are well prepared to take AS310 Exam 3

“WHAT”

Flowchart for Computing Max Gross Takeoff Weight and V-Speeds

Flowchart for Climb Improvement and VMBE Check

“WHY”

Field Limit Weight—if critical engine fails at V1, allows

·  attaining 35’ AGL and V2 by the end of the runway

·  stopping on the remaining runway without using reverse thrust

Obstacle Limit Weight—allows obstacle clearance at V2 during the 2nd segment

Tire Limit Weight—protects tires against failure before rotation due to stress resulting from

·  centrifugal force stress that increases as ground speed increases

·  weight stress on wheels that increases as takeoff weight increases

This weight goes down as VR increases

Climb Limit Weight—allows meeting Part 25 minimum climb gradient requirements with the critical engine out, with particular emphasis on climb at V2 during the 2nd segment

V2

·  a compromise between what is desirable (VXSE, VYSE) and what is practical to attain between the end of the runway with the critical engine failed at V1

·  allows adequate climb capability in 2nd segment

Climb Improvement

·  possible only if climb limit weight is lowest (i.e. if aircraft is climb limited)

·  presumes additional runway length (field limit weight > climb limit weight)

·  presumes additional tire strength (tire limit weight > climb limit weight)

·  can add extra weight (climb improvement) and increase V2

·  increasing V2

o  makes V2 closer to VXSE, VYSE and thus makes the airplane climb “better”

o  thus still gives adequate climb capability in 2nd segment at the climb improved weight (climb limit weight + climb improvement)

VMBE—maximum speed to minimize brake fire possibility after T/O rejection

·  must not be smaller than V1—otherwise must reduce T/O gross weight

·  taking off weight reduces V1 and increases VMBE

·  if proper weight is removed, V1 and VMBE should be the same

PLEASE COMPLETE THE ONLINE AS310 COURSE EVALUATION

·  Your input provides very important feedback for the Air Science Department and the course instructor

·  Before you complete the evaluation, please ask yourself

1.  Were the extensive online learning materials complete, professional, and helpful to you in your learning efforts?

2.  Did you learn information that will make you a better aviation professional?

3.  Did you find the group activities helpful to your learning efforts?

4.  Did the course provide the right balance between lectures and group activities?

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