AEROWAY TECHNICAL REFERENCE
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AEROWAY.ORGREF-01
Aeronautical Reference Architecture
Flight Planning & Performance Hub →FAA ORDER 8260.3F (TERPS) • FAA-H-8083-16B • 14 CFR § 25.121 • ICAO PANS-OPS

Climb Gradient & Obstacle Clearance Calculator

Convert climb gradients in feet per nautical mile (ft/NM) and percentages to required vertical speeds (FPM) and climb flight path angles. Evaluate Departure End of Runway (DER) screen heights, 40:1 Obstacle Clearance Surfaces (OCS), and transport category single-engine inoperative (OEI) climb minimums.

Climb Gradient & Obstacle Clearance Solver

KTS
Speed Presets:
1. Climb Gradient Parameters
ft/NM
100 ft/NM (1.6%)200 ft/NM (Standard TERPS)500 ft/NM (8.2%)800 ft/NM (13.2%)
2. Departure End of Runway & Obstacle Analysis
3. Level-Off Altitude (Top of Climb)

Enable to calculate exact horizontal distance (NM) and elapsed climb time (min:sec) to reach your departure transition altitude or MEA.

Climb Gradient & Obstacle SummaryCALCULATED CLEARANCE: +185 FT (MODEL)

At 120 kt groundspeed, maintaining a 200 ft/NM (3.29% / 1.89°) climb gradient requires a vertical speed of 400 FPM. Calculated climb profile crosses obstacle location at 1635 ft MSL, yielding a mathematical margin of +185 ft above the entered 1450 ft MSL obstacle.

Vertical Speed
400 FPM
@ 120 kts Groundspeed
Climb Gradient
200 ft/NM
3.29% Gradient
Climb Angle
1.89°
Slope: 30.4:1
Obstacle Crossing: 3 NM @ 1450′ MSL+185 ft margin
Crossing Alt:1635 ft MSL
Min Gradient:138.3 ft/NM
Min FPM @ 120kt:277 FPM
Departure Climb & TERPS Obstacle Profile
CALCULATED CLEARANCE: +185 FT (MODEL)
1.0 NM2.0 NM3.0 NM4.0 NM5.0 NM+500′+1000′+1500′+2000′RUNWAYDER (35′ screen)40:1 OCS (152 ft/NM)θ = 1.9°OBSTACLE (3 NM)1450′ MSL+185′ marginDistance from DER (NM) →↑ Altitude Above DER (ft)
Required Gradient200 ft/NM(3.29%)
Vertical Speed400 FPM@ 120 kt
Climb Angle1.89°(30.4:1)
Obstacle Margin+185 ft
⚠️Pilot in Command Notice (14 CFR § 91.3 / § 91.103): Required climb gradients are ground-referenced. For a fixed required ground gradient, a headwind reduces groundspeed and therefore reduces the FPM required to achieve that gradient; a tailwind increases groundspeed and increases the required FPM. Wind alters ground path geometry, not aerodynamic rate of climb. Always verify actual aircraft climb capability against density altitude in the approved AFM/POH.
Instrument Flight Procedures & TERPS Criteria

Anatomy of an IFR Departure & Obstacle Clearance Surface

In instrument flight operations, climb requirements are published as a climb gradient (ft/NM or %) rather than a fixed rate of climb (FPM). A climb gradient represents a geometric slope relative to the ground, ensuring positive obstacle clearance regardless of aircraft groundspeed or headwinds:

1. Departure End of Runway (DER)

The standard climb profile begins at the Departure End of Runway (DER) crossing at a screen height of 35 feet AGL (FAA TERPS) or 16 feet AGL (ICAO PANS-OPS), assuming no early turns before 400 ft AGL.

2. 40:1 Obstacle Clearance Surface (OCS)

Procedure designers construct a 40:1 sloping plane (152 ft/NM or 2.5%) beginning at the DER elevation. If no obstacles penetrate this surface, a standard departure is authorized.

3. Standard 200 ft/NM Gradient (ROC)

The standard climb gradient of 200 ft/NM (3.3%) incorporates the 152 ft/NM OCS plus 48 ft/NM (24%) of Required Obstacle Clearance (ROC) to provide a safety margin over terrain.

Aeronautical Climb Gradient & Obstacle Equations

MATHEMATICAL SPECIFICATIONFAA Order 8260.3F (TERPS), FAA-H-8083-16B, 14 CFR § 25.121
Gradient Conversions & Geometric Slopes (FAA Order 8260.3F / TERPS)
VSFPM=(Gradientft/NM × GSkts) / 60[Vertical Speed, FPM]
Gradientft/NM=(VSFPM × 60) / GSkts[Climb Gradient, ft/NM]
Gradient%=(Gradientft/NM / 6076.1155) × 100[Rise Over Run Percentage]
θangle=arctan(Gradientft/NM / 6076.1155)[Climb Flight Path Angle, Degrees]
Altcrossing=DERelev + ScreenHeight + (Gradientft/NM × DNM)[Aircraft Altitude at Obstacle]

Physical Variables & Aviation Unit Definitions

SymbolParameterPhysical MeaningUnit
VS_FPMVertical SpeedRequired rate of climb on the vertical speed indicatorFPM
GradientClimb GradientVertical climb per horizontal distance travelledft/NM or %
GSGroundspeedActual speed across the surface (TAS adjusted for wind)knots
θClimb AngleGeometric flight path angle above the horizontal horizondegrees
D_NMObstacle DistanceHorizontal distance from Departure End of RunwayNM
Standard Pilot Reference Table

Rate of Climb (FPM) Table vs. Climb Gradient & Groundspeed

Required vertical speeds (FPM) across common departure groundspeeds and published climb gradients (zero-JS static table):

Groundspeed (kt)200 ft/NM (Standard)250 ft/NM (4.1%)300 ft/NM (4.9%)350 ft/NM (5.8%)400 ft/NM (6.6%)500 ft/NM (8.2%)
60 kts200 FPM250 FPM300 FPM350 FPM400 FPM500 FPM
75 kts250 FPM313 FPM375 FPM438 FPM500 FPM625 FPM
90 kts300 FPM375 FPM450 FPM525 FPM600 FPM750 FPM
105 kts350 FPM438 FPM525 FPM613 FPM700 FPM875 FPM
120 kts400 FPM500 FPM600 FPM700 FPM800 FPM1000 FPM
135 kts450 FPM563 FPM675 FPM788 FPM900 FPM1125 FPM
150 kts500 FPM625 FPM750 FPM875 FPM1000 FPM1250 FPM
180 kts600 FPM750 FPM900 FPM1050 FPM1200 FPM1500 FPM
210 kts700 FPM875 FPM1050 FPM1225 FPM1400 FPM1750 FPM
240 kts800 FPM1000 FPM1200 FPM1400 FPM1600 FPM2000 FPM
300 kts1000 FPM1250 FPM1500 FPM1750 FPM2000 FPM2500 FPM
Checkride Step-by-Step Proof

Worked Example: Aspen (KASE) SADDL Departure Mountain Obstacle Analysis

Scenario: You are departing Runway 33 at Aspen-Pitkin County Airport (KASE, DER elevation 7,820 ft MSL). The published SADDL Obstacle Departure Procedure requires a minimum climb gradient of 460 ft/NM to 14,000 ft MSL. A controlling mountain ridge rises to 9,850 ft MSL at 4.5 NM from the DER. Your aircraft climb groundspeed is 130 knots.

Step 1: Calculate Required Rate of Climb (Vertical Speed FPM)

• VS = (460 ft/NM × 130 kts) / 60 = 996.67 FPM (Target: ≥ 1,000 FPM on VSI).
• Climb Angle θ = arctan(460 / 6076.12) = 4.33° (13.2:1 slope ratio).

Step 2: Calculate Aircraft Altitude at Mountain Ridge (4.5 NM)

• Altcrossing = DER (7,820 ft) + Screen Height (35 ft) + (460 ft/NM × 4.5 NM)
• Altcrossing = 7,855 + 2,070 = 9,925 ft MSL.

Step 3: Evaluate Terrain Clearance & Margin

• Vertical Margin = 9,925 ft − 9,850 ft (Ridge Peak) = +75 ft clearance above obstacle.
• Conclusion: Meeting the 460 ft/NM gradient clears the ridge. If high density altitude limits your climb rate below 1,000 FPM, an IFR departure is not authorized.

Aerodynamic & Meteorological Dynamics

Wind Component & Density Altitude Impact on Climb Gradients

Why indicated airspeed (IAS) climb performance in the POH differs from ground-referenced departure gradients:

Atmospheric VariableEffect on Groundspeed (GS)Effect on Climb Gradient (ft/NM)Required VSI Adjustment
Headwind on DepartureDecreases GSSteepens Gradient (More altitude per NM)Lower FPM needed to meet published ft/NM.
Tailwind on DepartureIncreases GSFlattens Gradient (Less altitude per NM)Significantly Higher FPM required!
High Density AltitudeHigher TAS / GS for same IASFlattens Gradient (Engine thrust drops)Aircraft may fail minimum TERPS gradient.
FAA TERPS vs. ICAO PANS-OPS vs. Transport CS-25

International Departure Climb & Multi-Engine Gradient Standards

Standard CategoryFAA Requirement (United States)ICAO / EASA Requirement (International)
Standard IFR Departure Gradient200 ft/NM (3.3%) (FAA Order 8260.3F TERPS).3.3% (200.5 ft/NM) (ICAO Doc 8168 PANS-OPS).
DER Crossing Screen Height35 ft AGL at Departure End of Runway.16 ft (5 m) AGL (ICAO standard screen height).
Obstacle Clearance Surface (OCS)40:1 (152 ft/NM / 2.5%) with 24% ROC buffer.2.5% (152 ft/NM) with 0.8% Procedure Design Margin.
Part 25 Transport 2nd Segment OEITwin: 2.4% • Tri-Jet: 2.7% • Quad: 3.0% (14 CFR § 25.121).Twin: 2.4% • Tri-Jet: 2.7% • Quad: 3.0% (EASA CS-25.121).
Checkride Oral Examination Guide

Top 5 DPE Checkride Questions: Climb Gradients & Obstacle Clearance

Standardized oral exam questions asked by Designated Pilot Examiners (DPEs) during Instrument, Commercial, and ATP practical tests:

1. What assumptions are built into a standard FAA TERPS IFR departure procedure?▼

Under FAA Order 8260.3F, unless specified otherwise on the departure chart:

  1. Cross the Departure End of Runway (DER) at a screen height of at least 35 feet AGL.
  2. Climb on runway heading to at least 400 feet AGL before making any initial turn.
  3. Maintain a minimum continuous climb gradient of 200 feet per nautical mile (3.3%) until reaching the minimum IFR enroute altitude (MEA/MOCA).
2. Why does a published departure procedure specify climb gradient in ft/NM instead of FPM?▼

Obstacles and terrain are fixed physical objects on the earth's surface. A climb gradient in ft/NM establishes a fixed geometric slope over the ground.

Because aircraft groundspeed varies drastically with aircraft category and wind, specifying a fixed FPM would cause fast aircraft or aircraft with tailwinds to penetrate obstacle clearance surfaces. Converting ft/NM to FPM using actual groundspeed ensures all aircraft achieve the required obstacle clearance slope.

3. What is the difference between an Obstacle Departure Procedure (ODP) and a Standard Instrument Departure (SID)?▼

An Obstacle Departure Procedure (ODP) is designed solely for obstacle and terrain clearance. Under Part 91, ODPs are recommended and do not require an ATC clearance to fly unless assigned by ATC.

A Standard Instrument Departure (SID) is designed for ATC traffic management and flow in busy terminal areas, in addition to terrain clearance. SIDs require an explicit ATC clearance to fly.

4. What happens if your aircraft cannot meet a published non-standard climb gradient?▼

If an aircraft cannot meet a published non-standard climb gradient (due to high density altitude, heavy takeoff weight, or engine failure), the pilot must:

  • Depart under Visual Meteorological Conditions (VMC) climb to IFR altitude.
  • Use an alternate runway with lower climb requirements.
  • Reduce aircraft payload or fuel weight to increase climb rate.
  • Fly a published Visual Climb Over Airport (VCOA) procedure.
5. What are the four takeoff climb segments for transport category aircraft under 14 CFR Part 25?▼
  • 1st Segment: Liftoff (35 ft) to landing gear full retraction at V2 speed. (Positive gradient for twins).
  • 2nd Segment: Gear up to minimum 400 ft AGL at V2 with takeoff thrust. (2.4% twin, 2.7% tri-jet, 3.0% quad).
  • 3rd Segment (Acceleration): Level off at 400+ ft to accelerate and retract flaps/slats.
  • Final Segment: Clean configuration climbing to 1,500 ft AGL at Max Continuous Thrust (1.2% twin, 1.5% tri, 1.7% quad).

Frequently Asked Questions

Multiply the climb gradient in ft/NM by your groundspeed in knots, then divide by 60: FPM = (Gradient × Groundspeed) / 60. For example, a 200 ft/NM gradient at 120 knots groundspeed requires exactly 400 FPM on your vertical speed indicator.

Aviation Workflow Handoffs

Upstream PrerequisiteProceed →

Assess Takeoff Density Altitude

Verify engine horsepower reduction and true airspeed departure climb penalties.

Upstream PrerequisiteProceed →

Solve Departure Climb Groundspeed

Determine actual climb groundspeed to evaluate headwind/tailwind gradient effects.

Related CalculatorProceed →

Calculate Descent Profile & TOD

Solve the descent half of your vertical navigation flight plan.

E6B Suite ModuleProceed →

Open in Master E6B Suite

Access the complete flight planning and navigation computer workstation.

Technical Basis & Governing Sources

View full source registry →
technical standardFAA Order 8260.3F

United States Standard for Terminal Instrument Procedures (TERPS)

Issuing Authority: Federal Aviation Administration (FAA)

Citations:
  • Volume 1, Chapter 2: General Criteria & Climb Gradients
  • Volume 4, Chapter 1: Departure Procedure Construction
  • Section 2-6: Obstacle Clearance Surface (40:1 / 152 ft/NM)
Official FAA/ICAO Document Reference
official handbookFAA-H-8083-16B

Instrument Procedures Handbook

Issuing Authority: Federal Aviation Administration (FAA)

Citations:
  • Chapter 1: IFR Takeoffs and Departures
  • Climb Gradient vs Rate of Climb Conversion
  • Obstacle Departure Procedures (ODP) & SIDs
Official FAA/ICAO Document Reference
regulatory14 CFR § 25.121

14 CFR § 25.121 — Climb: One-engine-inoperative (Transport Category Airplanes)

Issuing Authority: Federal Aviation Administration (FAA) / e-CFR

Citations:
  • § 25.121(a): Takeoff; landing gear extended (1st Segment)
  • § 25.121(b): Takeoff; landing gear retracted (2nd Segment: 2.4% / 2.7% / 3.0%)
  • § 25.121(c): Final takeoff segment
  • § 25.121(d): Approach climb
Official FAA/ICAO Document Reference
official handbookFAA-H-8083-25C

Pilot's Handbook of Aeronautical Knowledge

Issuing Authority: Federal Aviation Administration (FAA)

Citations:
  • Chapter 4: Principles of Flight
  • Chapter 8: Flight Instruments
  • Chapter 11: Aircraft Performance
  • Chapter 16: Navigation
Official FAA/ICAO Document Reference
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