What is MDA on Boeing 737? (Minimum Descent Altitude)

When it comes to aviation, safety is of paramount importance. Pilots are trained to adhere to strict guidelines and procedures to ensure the utmost security of the aircraft, crew, and passengers. One crucial aspect of flying that pilots must understand and follow is the Minimum Descent Altitude (MDA) for the Boeing 737-800 aircraft.

The MDA is the minimum altitude at which an aircraft can descend during an instrument approach. It is an essential reference point for pilots during landing and plays a critical role in maintaining a safe and controlled descent. Incorrectly overshooting or undershooting the MDA can have severe consequences, potentially leading to a loss of situational awareness or colliding with obstacles in the aircraft’s flight path.

Understanding the Minimum Descent Altitude

The MDA is specified for each instrument approach procedure and varies depending on several factors, including the runway’s elevation, approach speed, and weather conditions. It is typically established to provide pilots with enough altitude to visually identify the runway environment and continue the landing safely.

During an instrument approach, the pilot follows a pre-determined flight path defined by navigation aids such as radio beacons and Global Positioning System (GPS). The MDA is reached after descending from the final approach fix, which is usually the last point before intercepting the glide slope or localizer. At this point, the pilot transitions from using solely instruments to visual references to complete the landing.

It is important to note that the MDA is not the same as the decision altitude (DA) or decision height (DH). The DA or DH refers to the height at which the pilot must make a decision to either land or execute a missed approach if the required visual references are not met. The MDA is the minimum altitude the pilot can descend to in order to have a chance to establish visual contact with the runway environment and make an informed decision.

The MDA is typically expressed in feet above mean sea level (MSL). For the Boeing 737-800 aircraft, the MDA may range from as low as 200 feet AGL (Above Ground Level) to several hundreds of feet, depending on the specific instrument approach procedure and environmental conditions.

It is worth noting that the MDA may also be referred to as the Minimum Descent Height (MDH) when expressed in feet above ground level (AGL), particularly in some countries or regions. However, for the purpose of this article, the term MDA will be used.

Factors Influencing the Minimum Descent Altitude

The determination of the MDA for the Boeing 737-800 aircraft is influenced by various factors that pilots must take into account. These factors include:

1. Runway Elevation: The height of the runway above sea level affects the MDA. Higher runway elevations result in higher MDAs, providing pilots with additional altitude clearance.

2. Approach Speed: The aircraft’s approach speed influences the MDA. Higher approach speeds result in higher MDAs, giving pilots more time and distance to safely transition to the visual phase of the landing.

3. Weather Conditions: Weather conditions play a significant role in determining the MDA. Poor visibility, rain, fog, or other adverse weather conditions may necessitate a higher MDA to ensure sufficient visual contact with the runway environment.

4. Obstacle Clearance: The presence of obstacles along the flight path, such as mountains, buildings, or other structures, also affects the MDA. The MDA must be set at a height that allows for obstacle clearance while still providing enough altitude for the pilot to visually identify the runway environment.

It is important to note that the MDA is not fixed and can be adjusted based on these factors. The precise MDA for each instrument approach procedure is provided in the Boeing 737-800’s Flight Crew Operations Manual (FCOM) and other relevant documentation, ensuring pilots have the necessary information to execute a safe approach and landing.


The Minimum Descent Altitude (MDA) is a critical reference point for pilots flying the Boeing 737-800 aircraft during instrument approaches. It provides a minimum safe altitude at which a visual transition can be made from relying solely on instruments to visually identifying the runway environment. Understanding and adhering to the MDA is essential for pilots to maintain safety and ensure a successful landing.

The MDA is determined by various factors, including runway elevation, approach speed, weather conditions, and obstacle clearance. Pilots must consider these factors to ensure a safe descent and landing. The precise MDA for each instrument approach procedure is readily available in the aircraft’s documentation, supporting pilots in making informed decisions during their flights.

By following the guidelines and procedures related to the MDA, pilots can enhance the safety of their flights and instill confidence in passengers. The MDA serves as a crucial tool to mitigate risks during landing and contributes to the overall success of the aviation industry in prioritizing safety and security.

For More: What is SPM on Boeing 737? (Stabilizer Position Module)