Understanding Continuous Descent Final Approach (CDFA) in Aviation

What is Continuous Descent Final Approach (CDA)?

Continuous Descent Final Approach (CDA) is a technique for executing non-precision approaches through a constant, stabilized descent from the final approach fix to approximately 15 meters (50 feet) above the runway. Unlike the traditional ‘dive-and-drive’ approach. By eliminating disruptive level-off segments, CDA provides significant safety benefits.

The predictable flight path reduces pilot workload while enhancing safety margins. CDA has become the preferred method for achieving stabilized approaches.

The Traditional Non-Precision Approach Profile

The conventional ‘dive-and-drive’ non-precision approach follows a distinctly different pattern: descending to the Minimum Descent Height (MDH) after the final approach fix, then maintaining level flight. Pilots hold this altitude until visual contact with the runway is established, or the missed approach point is reached—a methodology that introduces several operational complications.

Multiple step-down fixes demand frequent adjustments to thrust, pitch, and altitude, increasing cockpit workload. The extended low-altitude level flight segment makes it difficult to achieve a stabilized approach configuration. This can precipitate rushed maneuvers when the runway finally becomes visible.

These intricate adjustments increase the risk of controlled flight into terrain (FIT) incidents, especially in challenging weather conditions or unfamiliar airports. Frequent transitions between descent and level flight phases create energy management challenges. This makes achieving a stabilized approach—a cornerstone of aviation safety—more difficult to achieve.

Risks of Unstabilized Approaches

Unstabilized approaches are a leading cause of Controlled Flight Into Terrain (FIT) accidents—one of aviation’s most devastating incident categories. Risk increases significantly on non-precision approaches featuring step-down fixes positioned inside the Final Approach Fix (FAF).

Key risks include:

• Increased Pilot Workload: Requiring simultaneous adjustments to thrust, pitch, and altitude during a critical flight phase increases the likelihood of errors.

• Reduced Safety Margins: Extended periods of level flight at low altitudes increase exposure to terrain and other hazards.

• Problematic Flight Profiles: Approaches can become too shallow or steep, making a stable transition to landing difficult.

• Rushed Final Maneuvers: Late runway acquisition may lead to aggressive attempts to align the aircraft, often without sufficient time to stabilize for landing.

Advantages of Continuous Descent Final Approach

The main safety benefit is achieving a genuinely stabilized approach through a constant descent angle. This unwavering profile reduces pilot workload by eliminating multiple altitude adjustments. It enhances situational awareness and significantly reduces FIT risk by ensuring consistent obstacle clearance.

CDA offers additional benefits beyond safety:

• Lower Fuel Consumption: Maintaining efficient power settings during a continuous descent burns less fuel than a step-down approach.

• Reduced Noise: The continuous descent profile is quieter overpopulated areas, making it more environmentally friendly.

• Regulatory Preference: Due to these combined advantages, aviation authorities worldwide encourage or mandate CDA.

How to Execute a CDA

Executing a CDA requires careful planning before reaching the Final Approach Fix (FAF). Pilots must calculate the precise rate of descent required to maintain a constant Vertical Descent Angle (VDA). This calculation hinges on three critical factors:

Execution commences by crossing the FAF at the predetermined altitude, ensuring the correct descent angle is established. Pilots then maintain the calculated descent rate without any leveling off. While vertical navigation (VSAV) systems can display the optimal path, this technique remains achievable using basic instruments by maintaining a constant vertical speed.

Throughout the descent, pilots continuously monitor the flight path, making subtle adjustments to maintain stabilization. The descent proceeds uninterrupted to approximately 50 feet above the runway threshold or flare point. Should visual contact remain unestablished by the Decision Altitude (DA)—derived from the Minimum Descent Height (MDH)—a missed approach becomes mandatory.

Regulatory Requirements for CDA

Although specific regulations vary across jurisdictions, most aviation authorities have similar basic requirements for CDA implementation. Operators typically must secure a specific Operations Specification (Ops Spec), demonstrating that appropriate procedures and training protocols are in place.

Key mandates typically include:

• Operations Manuals: Operators must integrate detailed CDA procedures, calculations, and techniques into their manuals.

• Comprehensive Training: Flight crews must receive thorough ground and simulator training on CDA execution.

A critical regulatory consideration involves converting Minimum Descent Height (MDH) to a Decision Altitude (DA). Many authorities mandate adding a safety buffer—commonly 50 feet—to the MDH. This buffer accounts for the aircraft’s momentum during continuous descent, ensuring the aircraft won’t descend below the MDH should a missed approach be initiated.

Further Reading and Resources

For more information of CDA, explore these authoritative resources:

• FAA Advisory Circular 120-108: Provides detailed guidance on CDA implementation, operational considerations, and best practices for U.S. operators.

• Airbus Safety First Magazine (#24, July 2017): Features in-depth articles on CDA techniques specific to Airbus aircraft, with practical tips for pilots.

• Flight Safety Foundation (ALAR Toolkit): Offers comprehensive materials on stabilized approaches, including briefing notes, videos, and training guides that highlight the safety benefits of CDA.