Transcript Slide 1

KC-135R/T Climb Gradient
More than you ever wanted to
know…
Capt Don Kennedy
55ARS/STM
Altus AFB, OK
Overview
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Purpose
Motivation
Review of Regulatory Requirements
Explanation of KC-135 Climb Gradient
Flap/Profile Selection
Effect of Speed Deviation on Climbout Flightpath
FSAS Techniques
Approach & Go-Around
Future Developments
Purpose
• To arm you with the knowledge and tools to
make sound takeoff planning decisions
• No imposition of my techniques or philosophy… I
want to help you develop your own
• However, give me the opportunity to sell you on
these ideas with facts and sound rationale
• Above all else… I WANT YOU TO THINK
Motivation
This discussion is not merely theoretical, designed solely to impress
your pilot friends at parties…
… it is designed to potentially save your life
Regulatory Requirements
AFI 11-202V3, General Flight Rules
Regulatory Requirements
AFI 11-2KC-135V3, C/KC-135 Operations Procedures
Regulatory Requirements
AFMAN 11-217V1, Instrument Flight Procedures
Regulatory Requirements
Aeronautical Information Manual, 5-2-6
“1. Unless specified otherwise, required obstacle clearance
for all departures, including diverse, is based on the pilot
crossing the departure end of the runway at least 35 feet
above the departure end of runway elevation, climbing
to 400 feet above the departure end of runway elevation
before making the initial turn, and maintaining a
minimum climb gradient of 200 feet per nautical mile
(FPNM), unless required to level off by a crossing
restriction, until the minimum IFR altitude.”
Regulatory Requirements
• T.O. 1C-135(K)R-1-1, Flight Manual Performance
Data, 1A3-20A, Climbout Procedure, Note 2
– “The minimum planned clearance over an obstacle is 1.0% of
the obstacle distance from the end of the runway.”
• 6076(.01)=60.76 or 61 feet/nm
• If your standard OIS was 152 feet/nm, then 152
+ 61 = 213
• Therefore, Boeing says that 213 feet/nm, or
3.5% is your minimum 3-engine climb gradient
Regulatory Requirements
• So what clearance
requirement am I
supposed to
satisfy?
• Kennedy’s Opinion
(Peacetime Criteria)
– 61’: Will satisfy if able
– 0’: Unsafe
– 48’: Appropriate
1400
213 (61)
1200
200 (48)
1000
Height Gain (ft)
– Boeing’s 61 feet?
– AIM’s 48 feet?
– AF’s 0 feet?
Obstacle Clearance Plains – Feet/NM (Height Above)
1600
800
152 (0)
600
400
200
Distance (OD) 152'/nm (2.5%)
Distance (OD) 200'/nm (3.3%)
Distance (OD) 213'/nm (3.5%)
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Distance from End of Runway (ft)
KC-135 Climb Gradient
• Climb Gradient… (Performance Data, 1A3-4)
– “Climb gradient is the flightpath climb angle expressed in percent,
and equates to feet climbed per 100 feet of horizontal distance
traveled.”
– “Climb gradient is a direct measure of the takeoff acceleration and
climb capability of the airplane.”
– “Climb gradient is used as a normalizing parameter to simplify
Part 3 performance charts.”
• So which is it?
– Height gain per distance traveled? (true climb gradient)
– Measure of performance?
– Normalizing parameter?
KC-135 Climb Gradient
• The answer is, “YES!”
• All three statements are true
– Height gain per distance traveled
– Measure of performance
– Normalizing parameter
• Boeing uses true climb gradient as a measure of
aircraft performance (thrust excess) to normalize
your takeoff data
• Normalizing… meaning climb gradient is the
parameter that accounts for temp, PA, gross
weight, thrust setting, etc. that characterize your
takeoff
KC-135 Climb Gradient
“Since climb gradient equates the feet climbed per
100 feet horizontal distance traveled, the climb
gradient can be used to find the minimum height
at a given obstacle distance. This method is
different than that used for obstacle clearance in
Part 3, where additional charts are needed to
determine obstacle clearance. The need for
additional charts is a result of the climbout
flightpath angle. This is not a constant value, and
thus one climb gradient cannot be assigned to it.”
- Boeing response to field visit questions, Sep 04
KC-135 Climb Gradient
• Although “True Climb Gradient” is perfectly
linear, airplanes do not fly straight-line flight
paths during the takeoff phase
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Changing pitch
Acceleration
Ground effect
Gear or flap retraction
Pilot technique
Thrust lapse rate
Changing environmental conditions with altitude
KC-135 Climb Gradient
• Okay, fine… all this theory is nice, but what I
really care about is HOW DO I USE IT???
• You are really interested in Climbout Flightpath
– “How high am I at a certain distance if I am trying to clear an
obstacle or maintain a min feet/nm?”
• DO NOT use the Climb Gradient the FSAS gives
you (i.e. 8%) as a direct measure of your ability
to meet your IFR climb criteria (feet/NM) or
ability to clear an obstacle
– Climb Gradient ≠ Climbout Flightpath
• Remember… your Climbout Flightpath is highly
non-linear, which is why we have flight-test data
for height above unstick
KC-135 Climb Gradient
• Proof that Climb Gradient ≠ Climb Gradient
• Conditions:
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205,000 lbs
27% C.G.
Temp: 25°C
PA: 1000
Winds: 030°/10
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Runway Length: 11,200’
20 Flap Accel Profile
Climb Gradient = 8%
UOD: 11,149’
OD: 6076’ (1 mile)
• If the jet really flew an “8% Climb Gradient,” at
1 mile from the end of the runway it should be
at least 486 feet high (6076 x .08 = 486)
KC-135 Climb Gradient
CHART USED IS SPECIFIC FOR EACH
T/O PROFILE AND FOR CLOSE IN VS.
DISTANCE OBSTACLES!
KC-135 Climb Gradient
330’
FSAS Calculator computed a DHT of 328’
KC-135 Climb Gradient
• If the jet really flew an “8% Climb Gradient,” at
1 mile from the end of the runway it should be
at least 486’ feet high (6076 x .08 = 486)
• Charts: 330’ FSAS: 328’
• 330 ft/nm = 4.9% “True Climb Gradient”
• Therefore, you can’t correlate the charted climb
gradient to a desired height vs. distance gained
for the purpose of obstacle clearance!
Flap/Profile Selection
• If the charted or FSAS-calculated Climb Gradient
is a measure of thrust excess, then the pilot can
use it in three ways:
– Climb
– Accelerate
– Both climb and accelerate (tradeoff)
• Selection of takeoff flap setting and profile then,
is just a decision about how to use your Climb
Gradient
– “How do I need/want to use my performance today?”
Flap/Profile Selection
• Performance Manual’s preference order
– 20 ACCL, 20 MAX, 30 MAX, 30 ACCL
– Pilot’s prerogative to choose
• What are some caveats to this precedence?
– Obstacle clearance
– Runway available
– Ground min control speed
• You must understand why you have selected a
particular flap setting and profile
– “We always do 20 ACCL at my base” is
unacceptable
Flap/Profile Selection
• Age old question… “What is the best flap setting
and profile?”
• The answer: “Well, that depends.”
• Factors to consider when selecting a profile
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Runway available
Runway end crossing requirements
Gross weight
Min IFR/SID climb gradient compliance
Obstacle clearance (and how far away the obstacle is)
Reduced thrust N1 setting
Controllability/stall margin
Operational/Training Requirements
Flap/Profile Selection
• Benefits of the ACCL mode takeoff
– Increased stall margin
– Quicker acceleration through region of reverse command
(quicker flap retraction)
– Improved controllability
– Improved distant obstacle clearance at lighter gross weights
– Improved windshear penetration
Flap/Profile Selection
• Pitfalls of the ACCL mode takeoff
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Relatively shallow initial climbout flightpaths
Close-in obstacle clearance is problematic
No way to validate FD109 pitch commands
More procedurally difficult during a critical phase of flight with
engine loss and/or FD109 failure
These qualities present an obvious safety concern, which is why some
advocate elimination of the ACCL profile. The arena in which the
ACCL mode shines (heavy/performance limited) is precisely where its
pitfalls render it illegal, unsafe or impractical, due to inadequate
obstacle clearance and an inability to validate the FD109-commanded
flightpath.
Flap/Profile Selection
• “So which flap setting is better for obstacle
clearance, 20 or 30?”
– Answer: “It depends!”
• 30 for close-in obstacles (less than ~3 miles)
• 20 for distant obstacles (greater than ~3 miles)
Climbout Flightpath Comparison - High Gross Weight
Flap/Profile Selection
2500
Gross Weight: 288K lbs
RA: 9700’
Temp: 20C
2000
PA: 1000’
Height Gain (ft)
N1: TRT
1500
1000
500
Distance (OD) 152'/nm (2.5%)
Distance (OD) 200'/nm (3.3%)
Distance (OD) 213'/nm (3.5%)
Distance (OD) 20ACCL
Distance (OD) 30MAX
Distance (OD) 20MAX
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Distance from End of Runway (ft)
Effect of Speed Deviation
• Your charted climbout flightpath is predicated
upon you correctly setting the computed takeoff
N1 and flying within the allowable speed
deviation
– 20 Flap: 8 knots
– 30 Flap: 3 knots
• Remember… for a fixed thrust setting,
acceleration comes at a price (less climb)
• Exceeding your speed deviation invalidates your
takeoff solution
Effect of Increased Rotation Speed of 10 Knots
500
Gross: 288K lbs
RA: 11800’
400
T: 30C
PA: 1000’
200'/NM
Height Gain (ft)
MCT: 89.4%N1
300
200
No tech order data for exceeding
speed dev… this example, using
increased rotation is anecdotal
evidence to illustrate what happens
when you exceed your speed
deviation
On Speed
+10kts
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Distance from End of Runway (ft)
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FSAS Techniques
• Alright Kennedy, I’m sick of theory… just show
me how not to hit stuff if I lose an engine on
takeoff!
• USE THE FSAS—it is easier!
• The Part 3 charts use Unstick to Obstacle
Distance (UOD) whereas the FSAS deals in
Obstacle Distance (OD) from end of runway
– This makes the FSAS easier, because IFR climb gradients and
published obstacles are given from the end of the runway
How to Use the FSAS
(Reference cheat sheet at end of slides)
How to Use the FSAS
How to Use the FSAS
The PC
version
does the
same
thing
How to Use the FSAS
• Use the FSAS iteratively to check your actual
climbout flightpath
– Runway end crossing height – “[OD/H] of [1/1]”
– Check at 1nm (6076 feet) or and at multiple points along your
flightpath until you are satisfied
• Your FSAS uses the 1% of obstacle distance rule
as an acceptable crossing height
– “T/O NOGO” will be displayed if DHT is less than 61’/nm
• Consider using the “1 foot obstacle technique”
– For example: for [OD/H] Enter [6076/1]
– Will yield an height above departure end of runway elevation
Future Developments
• SID Compliance Charts
– Will tell you what FSAS Climb Gradient you need to enter to
achieve a given published climb requirement
– Will help eliminate the highly iterative process of using the FSAS
DHT function or Part 3 charts
– Easier to determine runway end crossing height compliance
• Will drive gross weight reductions in some
cases to meet min IFR takeoff criteria
TRAINING/REFERENCE ONLY
Approach & Go-Around
• Misconceptions abound…
• Required Climb Gradient (real engine out)
– Missed approach… 11-202V3 & 11-217V1: 200’/nm or 3.3%
• But what about 11-2KC-135V3 9.6.2? (practice)
3.3%
– “2.8% @ touchdown speed, 30° Flaps, gear, …”
• If I put [1/4] for engines out in the FSAS, won’t
I get a symmetric 2E climb gradient? NO!
• Is that a 3.3% off the FSAS or is that 3.3% “true
climb gradient?”
Approach & Go-Around
• The answer is… YES!
• In this case, they are the same!
– Can I use the FSAS as direct measurement for missed approach
or go-around? YES!
• Yes… and Boeing explains it best:
– “The charts in Part 9 were built using a different method, one
using a “true” minimum climb gradient, which can be
conservatively used for obstacle clearance planning.”
• So if my FSAS reads 3.3 or higher, am I good?
• In reality, you have something greater, as the 3E
FSAS climb gradient is 50 Flap, not 30 Flap
Practice 3-Engine Work
• The issue typically isn’t meeting a 3.3% climb
gradient for 3E go-around performance at
transition weights
• The question you’re really concerned about is…
– When do I need to use the asymmetric throttle?
• If your 2E (same side) climb gradient is 3.3 or
above, then your actual climb gradient (with 2
engines at idle and the other 2 at symmetric N1)
will be something above 3.3
• If you don’t get 3.3 off the FSAS for 2E, you’ll
have to run the chart … Fig 1A9-8
The Bottom Line
• Peacetime: make every effort to meet 200’/nm
(or higher, if published) 3-engine
• Don’t use the Climb Gradient from the FSAS as a
direct measure of climb performance—use the
DHT iteratively to determine if you meet or
exceed the required climbout flightpath
• Fly ACCL takeoffs if you wish—just understand
that when conditions exist for its benefits to
shine, such benefit is negated by its limitations
• Don’t blow off your speed deviation when flying
a MAX mode profile—it is what validates your
obstacle clearance
KC-135R/T Obstacle Clearance Verification
The term “Climb Gradient” has two distinct means of application, that if
interchanged, could kill you. For example, if a SID requires a 400 feet/nm
climb (6.6% climb gradient) for obstacle clearance and your FSAS data says
you have a 8.0% climb gradient, you may or may not be able to clear that
obstacle. These two “climb gradients” are related, but only indirectly.
Therefore, do not directly equate one with the other!
Climb Gradient (1): (FAA, TERPS, AFI11-202V3, etc.) The flightpath climb
angle, expressed in percent, and equates to feet climbed per 100 feet of
horizontal distance traveled. For example, AFI11-202V3 requires a 200
feet/nm climb (all engines operating). If there are 6076.1 feet in 1 nautical
mile, then 200/6076.1 = 0.0329. Hence, the regulated minimum climb
gradient of 3.3%.
Climb Gradient (2): (Boeing) While the Performance Manual does state
that “climb gradient” is distance vs. height, this number, given by your FSAS
computer or performance charts, represents the “takeoff and acceleration
and climb capability of the airplane,” and is “used as a normalizing parameter
to simplify Part 3 performance charts.” Maybe Boeing should have used a
different term like “Climb Factor” to label this parameter. Nevertheless, think
of the climb gradient given by the box or the charts as a measure of thrust
excess… i.e. how well your jet will perform on a given day under specific
conditions (temp, PA, gross weight, etc).
How to compute climbout flightpath using charts… (geek method)
1. Determine the actual climb gradient from your FSAS computer or
performance charts (the climb gradient from your TOLD sheet or what
the box is reading… i.e. 8.0%)
2. Determine whether or not you have a “close-in obstacle” (0 to 8,000 feet)
or “distant obstacle” (8,000 to 40,000 feet). Remember… there are 6076
feet per nautical mile! For obstacles greater than 40,000 feet, (or about
6.5 miles) you must perform an enroute climb problem along with a
takeoff climb problem.
3. Determine your Unstick to Obstacle Distance (UOD). This is a fancy way
of saying, “how far is the thing you don’t want to hit from the point where
my jet leaves the ground and starts to climb?) UOD = (Runway Available
– Lineup Distance – Critical Field Length) + (obstacle distance from end
of runway). If you were a Poly Sci major and can’t do math, and you
want to “be conservative,” blow off this calculation and simply use the
obstacle’s published distance from the end of the runway as the UOD.
4. Open your performance manual to the appropriate chart… they start on
page 1A3-65. Be sure to pick the right chart for your flap setting
and takeoff mode!
5. Enter the respective chart at the bottom with the UOD you previously
calculated. Move up the chart to the climb gradient given by your FSAS
computer. Move right to read your “Height Above Unstick.”
For reference use only!!! Questions or comments, contact Capt Don Kennedy, 55ARS, [email protected]
6. The performance manual’s minimum clearance for an obstacle is 1% of
the obstacle distance from end of the runway. Add the minimum
clearance requirement to the obstacle height and compare it to your
height above unstick to determine if a safe takeoff may be accomplished
Note: If you are trying to clear an obstacle, you’re most likely flying a max
mode profile… so don’t forget that clean-up height is 2000 feet AGL or 120
percent of the obstacle height above unstick, whichever is higher.
What to do about a variable runway gradient?
All of the performance data charts used to determine height above unstick
have correction charts corresponding to your particular takeoff profile.
How to make sure I don’t hit nothin’… (pilot method using the FSAS)
1. Check your NOTAMS, AP1, IFR Sup, Approach Plate, etc. for published
obstacle information or required climb gradient. Realize that
performance charts deal with Unstick to Obstacle Distance (UOD)
while your FSAS (both on the jet and on your desktop calculator)
use Obstacle Distance from the end of the runway (OD).
2. Published obstacle information will typically depict an obstruction height
in feet and a distance from the end of the runway in nautical miles.
Once you convert the Obstacle Distance (OD) from NM to feet, you’re
ready to plug and chug! (Remember: 6076 feet per nautical mile!)
3. Published Technique: On the bottom, left-hand side of your Takeoff
Runway Data 1/7 Page, there is a spot for you to insert your obstacle
information (distance and height, as expressed in feet… [OD/H]. After
you have run your data, (assuming it is a “GO”) you will see the height
at which you will clear the obstacle on your Takeoff Data 5/7 Page…
about half-way down on the right side of the CDU. It is labeled “DHT”
and stands for Delta Height Above Obstacle, up to 999 feet.
Question: So what if the box gives me a “Takeoff NO-GO” because
it determines that I can’t clear the obstacle? Good question… the
box does not tell you how close you are to clearing the obstacle.
Rather, it simply tells you whether or not a safe takeoff can be made.
Therefore, try this technique…
4. Recommended Technique: Simply enter the Obstacle Distance and
one foot on the Takeoff Runway Data 1/7 Page. For example, if you
had a 300 foot tower at 1nm, enter [6076/1] for OD/H. The box will then
tell you how many feet you will be over this “one foot” obstacle. It is
then up to you how much clearance you’ll accept… remember, the
Dash1 recommends 1% of OBSTACLE DISTANCE as an acceptable
margin of HEIGHT to clear an obstacle. This technique also works
great for determining your crossing height at the departure end of the
runway (for complying with Army and Civil field procedures). You can
use this technique to determine your height at various distances from
the end of the runway and derive a “climb gradient” to compare with
published SID climb requirements.