The instructor flying the Cessna 172 that overturned at John Wayne Airport in Santa Ana, California, on Saturday 7 November says the aircraft was struck by a sudden jet blast. In his report, shared by Orange County Flight Center with Flying Magazine, he describes the Cessna pitching forward and going over onto its back1. According to Flying, the United Airlines Boeing 737 ahead of the Cessna was adding power to enter Runway 02L at the time1. The FAA is investigating and has not determined a cause4. Our first report on the overturn covers the ADS-B data and how far the exhaust of a 737 MAX reaches.

The instructor's account

An instructor and a student were on board. Neither was hurt12. Speaking to CBS Los Angeles, the instructor said the Cessna had just started a left turn towards the parking area when the crew felt a sudden, strong airflow. "At that moment, we lost, completely, the control and the airplane started to tip over," he said3. He added that the school's aircraft usually stay on the opposite side of the runway, but the wind that day did not favour that direction, so they were parked closer to the entrance3. "We were scared. We were definitely scared," the student said3. Flying reports that the damage to the Cessna has not yet been fully assessed1.

The times given differ slightly. The flight school's report puts the event at about 14:40 local time1, while the FAA says about 14:304. The last ADS-B position from the Cessna was received at 14:36:48, just after the 737 started to roll5.

Officials have not named a cause

The FAA statement is unchanged since Saturday. It says the Cessna was blown over while taxiing behind United Flight 2611 and that the FAA will investigate4. An airport spokesperson told AVweb there were no injuries, no impact on operations and that the investigation is ongoing2. Airport officials first cited high winds, and the Orange County Fire Authority declined to say whether weather or jet blast caused the overturn2. The NTSB has not announced whether it will open its own investigation.

The flight school also points at the airfield itself. Its director says a major reconstruction and realignment project is under way at the airport, that general aviation is being adversely affected and that flight safety may be jeopardised2. The project is real. Contractor FlatironDragados is rebuilding and realigning Taxiway A, reconstructing connector Taxiways D and E and reworking a service road and an adjacent run-up area. The three-year, 102 million dollar programme is mostly carried out at night during planned closures6. Neither the airport nor the FAA has said whether the work put the Cessna closer to the 737.

Jet blast is not wake turbulence

The two hazards are often mixed up after an event like this. Wake turbulence is a product of lift. The AIM says an aircraft generates wingtip vortices from the moment it rotates on takeoff until touchdown7. A taxiing 737 leaves no wake. What reaches a light aircraft behind a jet on the ground is engine exhaust, and the rules for the two are very different.

Wake turbulence in the air is covered in detail. FAA Advisory Circular AC 90-23G tells pilots departing behind a larger aircraft to rotate before the point where that aircraft rotated and to stay above its climb path. After a larger aircraft makes a low approach, missed approach or touch-and-go, allow at least 2 minutes before your own takeoff or landing, or 3 minutes behind a Super8. Controllers give VFR pilots a "caution wake turbulence" advisory when they think wake may affect them89. Accepting traffic information or an instruction to follow another aircraft means you accept responsibility for wake avoidance yourself8.

Even in the air, little is fixed behind a 737. In FAA Order JO 7110.65, the controllers' handbook, the time intervals for departures on the same runway apply behind the heaviest consolidated wake turbulence (CWT) categories, plus a 2 minute interval for the lightest category behind a Boeing 75710. The 737 MAX 8 is CWT category F and the Cessna 172 is category I11. For that pair the order sets no time interval. A pilot can still ask for extra spacing, and the order says to do that before taxiing onto the runway10.

No minimum distance on the ground

For jet blast on ramps and taxiways there is no minimum distance at all. JO 7110.65 tells controllers to avoid clearances that require a Super or Heavy to use more than normal taxi power, and a 737 is neither. It also tells them to use caution when taxiing smaller aircraft near larger ones, and allows the phrase "caution jet blast" in a taxi clearance12. Whether that advisory was given to the Cessna crew has not been made public. The AIM puts the rest on the pilot, who should consider the effects of jet blast, prop wash and rotor wash during all ground operations13.

For student pilots and instructors at airports shared with airliners, the practical lesson is about timing. The blast is most likely to reach you when a jet starts to roll from a standstill or turns, because the exhaust swings with the tail. Hold at an angle behind a jet, not in line with it, and ask ground control to wait or for a different route if the geometry looks wrong. Take extra care when construction changes the usual taxi routes and parking spots. If you are preparing for flight training, ground operations and wake avoidance are part of every PPL course.