10.1 One/Two-Engine-Inoperative En Route Net Profiles & Driftdown

FAA Aircraft Dispatcher Certificate ADX

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1 Chapter 1: Regulations, Certification & Operational Control

1.1 Part 65 Subpart C: Certification, Eligibility & Currency 1.2 Operational Control & Dispatcher-PIC Joint Responsibility 1.3 Domestic, Flag & Supplemental Operations Framework 1.4 Dispatch Release Elements, Signatures & Recordkeeping 1.5 Regulations, Manuals, Crew Qualifications, and Source Control

2 Chapter 2: Atmospheric Physics, Pressure Systems & Fronts

2.1 Atmospheric Structure, Standard Atmosphere & Altimetry 2.2 Air Masses, Frontal Systems & Frontogenesis 2.3 Atmospheric Stability, Lapse Rates & Cloud Formation 2.4 Earth Motion, Regional Weather, Local Winds, and Water Phase Changes

3 Chapter 3: Aviation Weather Hazards & Severe Weather Avoidance

3.1 Structural and Induction Icing: Types, Accretion & Operations 3.2 Thunderstorms, Squall Lines, Microbursts & Low-Level Windshear 3.3 Clear Air Turbulence (CAT), Mountain Waves & Jet Streams 3.4 Low Ceilings, Fog Types & Visibility Restrictions 3.5 Hurricanes, Typhoons, Tornadoes, and Tropical Dispatch Hazards

4 Chapter 4: Weather Observations, Forecasts & Advisories Decoding

4.1 METAR and SPECI Surface Observations: Decoding & Operations 4.2 Terminal Aerodrome Forecasts (TAF): Groups & Timing 4.3 Pilot Weather Reports (PIREP): Coding, Severity & Urgent Alerts 4.4 In-Flight Advisories: AIRMETs, SIGMETs & Convective SIGMETs 4.5 Weather Collection, NWS Facilities, GFA, and EWINS

5 Chapter 5: Aviation Weather Charts & Upper-Air Analysis

5.1 Surface Analysis & Radar Summary Charts 5.2 Constant Pressure Analysis & Winds Aloft (FB) 5.3 Significant Weather Prognostic Charts (SIGWX) 5.4 Satellite Imagery, Moisture-Stability Analysis, and Forecast Integration

6 Chapter 6: Air Navigation, Airspace Architecture & Route Structure

6.1 National Airspace System: Classes, Rules & Special Use 6.2 Ground-Based Navigation Aids & Standard Service Volumes 6.3 Area Navigation (RNAV), GNSS/GPS, PBN & RNP Fundamentals 6.4 En Route Airways, SIDs, STARs & Chart Interpretation 6.5 Earth Coordinates, UTC, Chart Projections, and Flight Instruments 6.6 North Atlantic, Pacific, RVSM, and Global Navigation Differences

7 Chapter 7: Instrument Approaches, Minimums & Airport Operations

7.1 Precision Approach Systems: ILS Categories & Tolerances 7.2 Non-Precision Approaches, RNAV & Decision Minimums (MDA/DA) 7.3 Takeoff Minimums, Lower-Than-Standard & Takeoff Alternates 7.4 Holding Procedures: Patterns, Speed Limits & Timing

8 Chapter 8: Subsonic Aerodynamics & Jet Aircraft Performance

8.1 Subsonic Jet Aerodynamics: Lift, Drag & Flight Regimes 8.2 High-Altitude Flight: Mach Number, Buffet & Coffin Corner 8.3 Transport Turbine Engines: Thrust, Specific Fuel & Bleed Air

9 Chapter 9: Transport Category Takeoff & Landing Runway Analysis

9.1 Takeoff Performance Speeds & Balanced Field Concept 9.2 Takeoff Climb Segments & Obstacle Clearance Gradients 9.3 Landing Performance: Field Lengths, 60% Rule & Contamination

10 Chapter 10: En Route Performance, Driftdown Profiles & ETOPS Operations

10.1 One/Two-Engine-Inoperative En Route Net Profiles & Driftdown 10.2 Extended-Range Operations (ETOPS): Philosophy & Regulations 10.3 ETOPS En Route Alternates: Adequate vs. Suitable & Critical Fuel

11 Chapter 11: Aircraft Weight & Balance, Center of Gravity, and Loading

11.1 Transport Aircraft Structural Weight Limits: Definitions & Rules 11.2 Center of Gravity Computations: Datum, Arm, Moment & Index 11.3 Mean Aerodynamic Chord (%MAC) Computations & Stability 11.4 Payload-Range Analysis, Zero Fuel Weight Tradeoffs & Loading

12 Chapter 12: Destination Alternate Airport Selection & Weather Rules

12.1 Destination Alternate Selection: 91.169 & Part 121 1-2-3 Rule 12.2 Flag & Supplemental Operations Destination Alternate Rules 12.3 Derived Alternate Minimums: 1-Nav and 2-Nav Facility Rules

13 Chapter 13: Part 121 Fuel Planning, Reserves & En Route Re-Release

13.1 Part 121 Domestic Fuel Requirements: Reserves & Calculations 13.2 Part 121 Flag Fuel Requirements: 10% Reserve & Island Rules 13.3 Supplemental Fuel Requirements & Holding Fuel Management 13.4 Redispatch and En Route Re-release Procedures

14 Chapter 14: Transport Systems, Pressurization & MEL/CDL Procedures

14.1 Transport Jet Auxiliary Power, Electrical, Hydraulic & Pneumatic Systems 14.2 Cabin Pressurization, Rapid Decompression & Oxygen Requirements 14.3 Master Minimum Equipment List (MMEL), MEL & CDL Procedures 14.4 Flight Controls, Autoflight, Fuel, Oil, Brakes, and Fire Protection

15 Chapter 15: Hazardous Materials, Duty Regulations & Emergency Procedures

15.1 Dangerous Goods Carriage by Air (49 CFR Part 175) & NOTOC 15.2 Dispatcher Duty Limitations, Rest Requirements & Fatigue 15.3 Emergency Authority, Declaration & Diversion Decision-Making 15.4 NTSB Part 830 Accident Reporting & Wreckage Preservation 15.5 Security, Overdue Aircraft, and FAA Emergency Services

16 Chapter 16: Communications, ATC, and Flight Plan Procedures

16.1 Voice, Data Link, Position Reports, and Lost Communications 16.2 ATC Facilities, Separation, ICAO Flight Plans, and Traffic Management

17 Chapter 17: Human Factors and Practical Dispatch Applications

17.1 Dispatch Resource Management, Human Error, and Risk Decisions 17.2 Manual Flight Planning, PIC Briefing, Flight Watch, and Postflight Closeout

10.1 One/Two-Engine-Inoperative En Route Net Profiles & Driftdown

Key Takeaways Explain This Topic AI

§ 121.191(a)(1) requires positive slope at least 1,000 feet above terrain in the specified corridor.

§ 121.191(a)(2) uses a net path with at least 2,000 feet terrain clearance to a qualifying landing airport.

The applicable airport positive-slope height is generally 1,500 feet for modern certification dates, not 2,000 feet.

Five statute miles are approximately 4.34 NM; check the corridor on each side of track.

Driftdown speed and altitude come from the approved aircraft data; ETOPS and terrain compliance are separate checks.

Last updated: October 2026

Engine-Inoperative Enroute Performance and Driftdown

A flight that can cruise over mountains with all engines operating may lack sufficient performance after an engine failure. Dispatch planning must examine the approved net enroute flight path , the temperature and winds expected, and the route to a suitable landing airport. The one-engine rule in § 121.191 and the applicable two-engine rule in § 121.193 are different from an ordinary all-engine airway MEA check.

Gross, net, and aircraft-specific data

Gross performance describes the demonstrated aircraft performance basis. Net performance includes the prescribed reduction for planning safety margin. The dispatcher uses approved AFM net data with the correct weight, engine state, airspeed schedule, atmosphere, and configuration. Do not combine a gross ceiling with a net terrain-clearance requirement and call the calculation conservative.

For modern turbine transports, § 121.191 provides two compliance alternatives. Both start with a takeoff weight that, after normal fuel and oil consumption, satisfies the approved one-engine-inoperative enroute data. The operator must use expected ambient temperature. A standard-day diagram alone is insufficient when the forecast is substantially warmer than standard.

Alternative 1: positive-slope route evaluation

Under § 121.191(a)(1) , the approved net path must have a positive slope at least 1,000 feet above all terrain and obstructions within five statute miles on each side of the intended track . For airplanes certificated after August 29, 1959, there is also a positive-slope requirement at 1,500 feet above the airport at which landing after an engine failure is assumed.

This branch does not add a universal 2,000-foot terrain-clearance requirement from the other branch. The test is positive net climb capability at the specified terrain-relative altitude, together with the applicable airport condition. Showing that a driftdown path clears a ridge by 2,000 feet is not the same calculation as demonstrating positive slope at 1,000 feet above every relevant obstacle.

Alternative 2: net path to a landing airport

Under § 121.191(a)(2) , the net path must permit continuation from cruise to an airport meeting § 121.197, clearing terrain and obstructions within five statute miles of track by at least 2,000 feet vertically . The airport positive-slope requirement is 1,000 feet , or 1,500 feet for the certification dates specified in the regulation. It is not 2,000 feet above the alternate elevation.

Paragraph (b) adds assumptions: failure at the most critical point; the prescribed relationship to the critical obstruction and an approved navigation fix unless another safeguarded procedure is authorized; an approved adverse-wind method; permitted fuel-jettison conditions where applicable; a specified alternate meeting required weather; and fuel/oil consumption consistent with the approved net data.

Evaluation Terrain requirement Airport positive-slope requirement for modern applicable aircraft

§ 121.191(a)(1) Positive slope at least 1,000 ft above terrain in the specified corridor 1,500 ft above the assumed landing airport

§ 121.191(a)(2) Net path clears terrain by at least 2,000 ft in the specified corridor 1,500 ft above the assumed landing airport

Driftdown procedure and route geometry

Driftdown is the descent needed when the remaining engine capability cannot sustain the original cruise altitude. The crew follows the aircraft's approved engine-out speed and thrust schedule, commonly using maximum continuous thrust with a performance-efficient speed. Do not equate every approved driftdown speed exactly with maximum L/D or prescribe a universal FL220 endpoint. Weight, atmosphere, engine state, and aircraft design determine the profile and stabilized altitude.

A driftdown decision point distinguishes the appropriate escape route after failure at different positions. If returning clears a western ridge but continuing clears an eastern ridge, the dispatch analysis must establish where each option remains valid. The critical point need not be the midpoint or the equal-time point between airports. A route's highest ridge also need not be its most restrictive obstacle after considering descent distance and winds.

Worked terrain comparison

Use a hypothetical airport at 4,000 feet MSL and a modern aircraft subject to the 1,500-foot airport condition. A positive-slope airport check is then at 5,500 feet MSL . If a ridge is at 12,000 feet MSL, the alternative-2 path must be at least 14,000 feet MSL at the relevant crossing. These are two separate comparisons with different reference surfaces.

Five statute miles equal about 4.34 nautical miles . Evaluate the entire prescribed corridor on each side of the route, including a ridge offset from the centerline. A planner using a five-NM corridor may be conservative in width, but a planner checking only the centerline can miss a legally relevant obstruction. Keep chart units explicit and use the approved route-analysis method.

Two-engine-inoperative requirements

For aircraft subject to § 121.193(c) , the route must either remain within 90 minutes at all-engines-operating cruise power of an airport meeting § 121.197, or satisfy the prescribed two-engine-inoperative net path. That path clears the five-statute-mile corridor by 2,000 feet, has positive slope at 1,500 feet above the landing airport, and includes the required arrival and 15-minute cruise fuel conditions. Earlier certification-date branches have different wording and must be read separately.

The 90-minute performance-rule alternative is not the twin-engine ETOPS 60-minute definition. Do not use one threshold to answer the other question. A twin's ETOPS route and critical fuel assessment also do not automatically prove terrain clearance after failure.

Combine failure scenarios responsibly

An engine-out plan assumes a particular cabin-pressure state. A simultaneous depressurization can require a lower altitude or an oxygen-compliant escape profile over high terrain. Evaluate it with approved oxygen and ETOPS fuel data where applicable. Do not promise that the aircraft can immediately descend to 10,000 feet when mountains obstruct that level.

Before release, crosscheck temperature, wind, ice/anti-ice penalties, weight at critical points, airport weather and performance, and the recorded escape route. During flight, updated weather or aircraft status can invalidate the planned assumptions. Provide timely information to the PIC and reassess the route; the dispatcher supplies operational support while the crew executes the aircraft-specific abnormal procedure.

Official References

Source check: 2026-10-12 . Engine-out performance § 121.191 ; ETOPS alternates § 121.624 ; ETOPS fuel § 121.646 ; ETOPS maintenance § 121.374 . For operational use, apply current issued authorizations and the assigned aircraft’s approved data.