NTSB Blames Controller After Allegiant Jet Nearly Hits Cessna on Takeoff — 100 Feet From Fatal Crash

The 100-Foot Allegiant–Cessna Near Midair Collision

On April 29, 2021, Allegiant Air Flight 803, an Airbus A319 operating from St. Petersburg-Clearwater International Airport, came within 100 feet vertically of a Cessna 337 operating in the airport traffic pattern. The incident became the subject of an NTSB investigation into controller scanning, pilot decision-making and runway separation.

The Cessna 337, registered N370SD, was flying a right downwind for runway 22 at about 300 feet. At the same time, Allegiant 803 was departing runway 18 and was at approximately 200 feet. The two flight paths intersected over the runways.

The Allegiant crew saw the Cessna and took evasive action. The A319 stopped its climb at about 200 feet and passed underneath the Cessna, which was at approximately 300 feet. Radar data later established that the closest separation was about 100 feet vertically and 369 feet laterally.

The NTSB found failures on both sides of the traffic-management picture. The local controller did not fully scan the runways and local airspace when issuing the Cessna's downwind instruction and again when clearing the Allegiant flight for takeoff. The Cessna pilot also flew a downwind that was significantly closer to the runway than the standard half- to one-mile pattern distance and did not maintain the standard traffic-pattern altitude.

The airport did not have a charted traffic-pattern altitude, which was also relevant to the investigation. The combination meant that an aircraft expected to remain outside the departure corridor was physically much closer to the runway intersection than the controller anticipated.

The NTSB's probable-cause finding placed primary responsibility on the air traffic controller's failure to scan the runway and local area, which resulted in a loss of situational awareness and failure to ensure separation. The Cessna pilot's poor decision-making was identified as a contributing factor.

The incident is particularly instructive because both aircraft were operating normally. There was no engine failure or weather emergency forcing the conflict. The hazard arose from the interaction of traffic-pattern geometry, controller scanning and assumptions about where each aircraft should have been.

The Allegiant crew's visual acquisition of the Cessna provided the final layer of defense. Had the A319 crew not seen the aircraft and stopped the climb, the vertical separation could have disappeared completely.

For airport operations, the event also shows why a controller's scan must be active rather than assumption-based. A clearance is not a substitute for confirming that the intended runway and surrounding airspace are clear. At the same time, pilots flying non-standard patterns can place themselves in positions where the controller's mental model no longer matches the aircraft's actual position.

The NTSB case therefore remains a useful study in shared situational awareness: the controller, the Cessna pilot and the airline crew each had different pieces of the traffic picture, and only the last-second visual intervention prevented a collision.

The runway geometry was central to the event. Runway 18 and runway 22 intersected within the operating area, so the position of an aircraft on a downwind for one runway could become relevant to an aircraft departing another. The controller's mental picture depended on the Cessna remaining where a normal pattern would place it.

The controller then issued the Allegiant takeoff clearance without detecting the Cessna's position. The NTSB's finding is particularly important here because the controller had responsibility for maintaining separation, but the investigation also recognized that the Cessna pilot's decisions made the traffic picture less predictable.

Once the A319 began its takeoff, the crews were suddenly confronted with a geometry that the controller had not fully resolved. The Allegiant pilots saw the Cessna and stopped their climb at about 200 feet. Because the Cessna was around 300 feet, the A319 passed beneath it rather than continuing upward into its path.

The measured separation—100 feet vertically and 369 feet laterally—shows how close the event became. For a transport-category aircraft accelerating through the departure phase, a 100-foot vertical difference is a very small margin.

The NTSB's final finding did not treat the event as the result of a single isolated mistake. The controller's scan failure was the probable cause, while the Cessna pilot's pattern and altitude decisions contributed. The airport's lack of a charted traffic-pattern altitude was another relevant circumstance.

That combination is instructive for both pilots and controllers. Controllers cannot safely assume that an aircraft is where a standard pattern would place it; pilots cannot assume that an unconventional pattern will be understood by everyone else in the traffic environment. The safest traffic pattern is one that is both predictable and actively monitored.

The incident ended without damage or injury, but the defensive chain was already being consumed. The controller had lost the expected picture, the Cessna was in an unexpected position, and the departing A319 had to rely on its crew's visual scan to prevent the encounter from becoming a collision.

The NTSB investigation consequently provides a detailed example of shared responsibility for traffic awareness. The system worked in the end because the airline crew detected the conflict, but the report makes clear that the conditions that produced the conflict should have been prevented much earlier.

The NTSB's detailed separation measurements make the event particularly valuable for training. A 369-foot lateral distance can sound large when expressed on a map, but it is extremely small relative to the wingspan, speed and energy of an Airbus A319. The vertical separation was even smaller.

The Cessna's altitude was also important. The standard pattern altitude would have created a different vertical picture, while the unusually tight downwind placed the aircraft close to the intersection of the two runway environments.

The controller's failure to scan all runways meant that the clearance sequence was built on an incomplete traffic picture. The controller was not merely unaware of one aircraft; the controller had lost the relationship between the Cessna and the runway from which Allegiant was about to depart.

After the event, the investigation could reconstruct the sequence because radar data, controller actions and crew reports provided independent sources. That reconstruction is precisely why near-miss investigations matter even when no one is injured: the system can be examined before the same chain produces a collision.

Accident Facts

Sources

• Video source (ATC/audio reconstruction)
• NTSB investigation OPS21LA002.
• NTSB operational-factors material.
• NTSB final probable-cause record.
• Video/ATC recording