Diversion Decisions (The Real Pickle)

A diversion is a landing somewhere other than the planned destination. The Pilot's Handbook: "There may come a time when a pilot is not able to make it to the planned destination. This can be the result of unpredicted weather conditions, a system malfunction, or poor preflight planning. In any case, the pilot needs to be able to safely and efficiently divert to an alternate destination" 1. The triggers are:

• weather that deteriorates ahead, or deteriorates behind and blocks the route back
• fuel below the planned reserve
• a sick passenger, or a sick pilot
• a rough engine, or a system the pilot no longer trusts
• a destination airport that closes, by its operating hours or by NOTAM
• lost situational awareness, a pilot who cannot say where the airplane is.

An early diversion costs least

The diversion decision costs least when the pilot makes it early. Each mile flown toward deteriorating conditions uses fuel, daylight, and options. The Risk Management Handbook gives an example of a pilot whose vacuum pump failed in visual conditions: "rather than divert to an airport while in VMC, the pilot decided to continue toward the destination and into instrument meteorological conditions (IMC)." The handbook's finding: "In this case, the pilot had the opportunity to change the outcome of the flight by diverting to an airport while still in VMC" 2.

A diversion made with an hour of fuel and an hour of daylight is a change of plans. The same diversion made with twenty minutes of each is an emergency. The rule is to divert while the diversion is still an inconvenience.

Personal minimums are the limits

A personal minimum is a number the pilot sets on the ground and applies in the air. The Risk Management Handbook: "Federal regulations that apply to aviation do not cover every situation nor do they guarantee safety. For example, a pilot may legally fly in marginal VFR conditions at night even though low visibility and night hazards increase the risk for an incident or accident. Therefore, pilots should consider non-mandatory self-regulation in the form of personal minimums." The handbook continues: "Established personal minimums enable the pilot to make a no-go or divert decision rather than departing with a sense of unease regarding the outcome of a flight. In addition, a written set of personal minimums can also make it easier to explain tough decisions to passengers who depend on the pilot's judgment" 3.

The pilot made the divert decision on the ground. The decision takes effect when any of these falls below its number:

• the ceiling
• the visibility
• the fuel
• the daylight.

The pilot in the airplane only carries out that decision.

The pilot chooses the alternate on six things. The handbook says to find the candidates before the flight: "Before any cross-country flight, check the charts for airports or suitable landing areas along or near the route of flight. Also, check for navigational aids that can be used during a diversion" 1. The six are:

• the weather at the alternate, now and by the time the airplane arrives
• the runway's length and surface against the Warrior's numbers
• the fuel to reach the alternate with the reserve still intact
• the terrain between the airplane and the alternate
• the services on the field: fuel, a telephone, weather reporting, someone there
• familiarity, because a pilot flies a known airport better under stress.

Nearest is not always best

The nearest airport is the right choice only when the emergency requires it. A strip two minutes closer, with no fuel, no phone, and no weather report, is the worse choice. A longer runway ten minutes farther, with all three, is the better one. The handbook's forced-landing advice makes the same point about fields: the pilot picks "a wind/obstacle/terrain combination that permits a final approach with some margin for error in judgment or technique" 4. With an engine running and fuel in the tanks, a few more minutes of flight provide that margin. With a rough engine or a sick passenger, the nearest usable runway is the right choice.

The diversion begins with a turn, not a calculation. The handbook: "in an emergency, divert promptly toward your alternate destination. Attempting to complete all plotting, measuring, and computations involved before diverting to the alternate destination may only aggravate an actual emergency" 5. The order is:

• fly the airplane through the turn to the new heading
• set an altitude that fits the new course, the terrain, and the clouds
• then do the math
• then make the radio call.

The math in flight

The pilot does the math in pieces, with shortcuts. The handbook: "When in flight, it is rarely practical to actually plot a course on a sectional chart and mark checkpoints and distances." The course "can also be measured with reasonable accuracy using a straightedge and the compass rose depicted around VOR stations." The handbook continues: "Once established on course, note the time, and then use the winds aloft nearest to your diversion point to calculate a heading and GS. Once a GS has been calculated, determine a new arrival time and fuel consumption" 5.

A pencil line on the chart gives the course. The sectional's scale, or the width of a thumb, gives the distance. The groundspeed gives the time, and the time gives the fuel. The pilot chooses the altitude for "cloud heights, winds, terrain, and radio reception" 5.

Replanning and the traffic scan

The replanning takes the pilot's attention inside the cockpit, away from the traffic scan. The AIM lists the first limit on the scan as "reduced scan frequency due to concentration on flight instruments or tablets and distraction with passengers" 6. The handbook's rule for the diversion: "Give priority to flying the aircraft while dividing attention between navigation and planning" 5. The pilot looks outside on a schedule. The pilot works the reroute in pieces of a few seconds each. The order aviate, navigate, communicate does not change.

The flight of N7763W

On November 25, 2023, at 6:35 in the evening, a Piper Cherokee 180 flew into the ground near Mertzon, Texas, in cloud, at night. The pilot, a 36-year-old private pilot with 94.7 hours, his wife, and their 10-year-old daughter died. The flight was from a family holiday in Las Cruces, New Mexico, home to San Antonio. The pilot had 4.5 hours of night time and 3.1 hours of simulated instrument time, and no instrument rating 7.

The weather brief that morning "included areas of marginal VFR and multiple Airman's Meteorological Information reports (AIRMET) for areas of instrument flight rules (IFR) conditions along the flight route that would be active during the airplane's passing time" 7. The pilot told his father the day before that the weather would be worse on Sunday, and that Saturday would be "a little cloudy." He filed for 10,500 feet and departed at 10 in the morning. He flew most of the first leg between 7,300 and 7,700 feet and landed at Pecos for fuel at 12:25.

The second leg began at 12:52 toward San Antonio. Within half an hour the airplane began changing heading and descending, at times to 3,100 feet. At 1:37 it turned around and flew 40 miles back west to Fort Stockton. On the way, "the pilot's wife texted his mother to report that they had turned around to go to Fort Stockton because the weather was not good," with a photograph of the airplane under a low cloud layer in visible moisture 7. That turn was a diversion, and it was the right decision. The airplane landed at 1:58.

At 2:31 they took off again on a new route. The airplane flew at 3,500 feet, began maneuvering again at 3:07, and at 3:36 turned to Reagan County Airport at Big Lake, landing at 3:40. That turn was a second diversion, also correct. There the pilot bought fuel "and then delayed the departure for about 2 hours and 38 minutes for unknown reasons." Sunset was 5:41.

They took off at 6:18, in the dark, toward hills. Ozona, 40 miles to the south, reported mist, a broken layer at 700 feet, and an overcast at 1,100 feet. The airplane flew between 3,000 and 3,900 feet and turned southeast. At 6:35 it entered a shallow descending left turn that tightened in its last four seconds. The NTSB found the data "consistent with spatial disorientation" and no mechanical failure. The probable cause: "The non-instrument-rated pilot's continued visual flight into night instrument meteorological conditions, which resulted in spatial disorientation and subsequent loss of control. Contributing to the accident was the pilot's overconfidence" 7.

Where the pilot could have prevented the accident

The pilot diverted twice and was right both times. The accident was the third diversion, the one the pilot did not make. Each decision below is marked with the PAVE category that applied to it.

A diversion changes the flight plan and often the ATC instruction the pilot follows. Both can change. The AIM: if a clearance "would place the aircraft in jeopardy, IT IS THE PILOT'S RESPONSIBILITY TO REQUEST AN AMENDED CLEARANCE. Similarly, if a pilot prefers to follow a different course of action, such as make a 360 degree turn for spacing to follow traffic when established in a landing or approach sequence, land on a different runway, takeoff from a different intersection, takeoff from the threshold instead of an intersection, or delay operation, THE PILOT IS EXPECTED TO INFORM ATC ACCORDINGLY" 8. Under 91.3 the pilot in command is the final authority, and in an emergency can deviate from any rule to the extent required 9.

The pilot tells ATC what the airplane needs. The pilot amends. The pilot does not leave the route without a call.

The controller and Flight Service

On flight following, the controller already sees the airplane on radar. ATC gives radar traffic information service to VFR flights "when requested by pilots of such flights," as the controller's workload allows 10. A controller who sees trouble issues a safety alert, after which "it is solely the pilot's prerogative to determine what course of action, if any, to take" 11. The call for a diversion gives three things:

• the position
• the intention
• the request, for vectors to the alternate, the weather ahead, or the airport's information.

Flight Service, on the radio, gives the weather ahead and the airport data in the same call. The pilot's own knowledge of the position and the alternates comes first. The controller's information is the cross-check.

The GPS "nearest" button

The GPS and the tablet find the nearest airport in one press. The handbook: "If GPS is installed, or a pilot has a portable aviation GPS on board, it can be used to determine the position and the location of the nearest airport." The limit: "In all cases, VFR pilots should never rely solely on one system of navigation. GPS navigation must be integrated with other forms of electronic navigation, as well as pilotage and dead reckoning" 12. The nearest list is a cross-check on the pilot's own knowledge of where the alternates are. A pilot who cannot name the alternate before pressing the button missed that step in the preflight.

The pilot protects the fuel reserve and does not spend it. A diversion that lands with the reserve intact is a correct diversion. A destination reached by burning into the reserve is a gamble that succeeded. It is still a gamble. The Pilot's Handbook's procedures for external pressure begin with fuel: "Allow time on a trip for an extra fuel stop or to make an unexpected landing because of weather" 13. Below the reserve, the flight is no longer the flight the pilot planned.

Minimum fuel

"Minimum fuel" is an advisory. The AIM: "Advise ATC of your minimum fuel status when your fuel supply has reached a state where, upon reaching destination, you cannot accept any undue delay. Be aware this is not an emergency situation, but merely an advisory that indicates an emergency situation is possible should any undue delay occur." The pilot says it after the call sign on first contact, and "a minimum fuel advisory does not imply a need for traffic priority." The next step is the emergency: "If the remaining usable fuel supply suggests the need for traffic priority to ensure a safe landing, you should declare an emergency due to low fuel and report fuel remaining in minutes" 14. The glossary: "This is not an emergency situation but merely indicates an emergency situation is possible should any undue delay occur" 15.

Minimum fuel tells the controller the airplane cannot accept a delay. The emergency, with minutes stated, gets the airplane on the ground first.

The solo brief

On a solo, no one else is aboard to notice the hesitation. The student prepares the diversion brief before takeoff: for each leg, the student names the alternate and the condition under which the airplane goes there. "If the ceiling is below 3,000 feet at the ridge, I land at the first airport on the near side." "If I am not at the checkpoint by 10:40, I turn back." The Risk Management Handbook's personal minimums are the source of the conditions 3. The student says the brief to the instructor, and the instructor asks for it before signing the solo.

External pressure is the main obstacle to a diversion. The Pilot's Handbook: "External pressures are influences external to the flight that create a sense of pressure to complete a flight—often at the expense of safety." Its list includes "someone waiting at the airport for the flight's arrival," "a passenger the pilot does not want to disappoint," and "the desire to satisfy a specific personal goal ('get-home-itis,' 'get-there-itis,' and 'let's-go-itis')" 16. The handbook ranks external pressure first among the risks: "Management of external pressure is the single most important key to risk management because it is the one risk factor category that can cause a pilot to ignore all the other risk factors" 13.

The counter

The counter is to make the alternate part of the promise. The Risk Management Handbook: "Because it may involve passengers or others waiting for the arrival, it is best to inform them of the need for flexibility," and for a flight with friends, "the pilot can reduce external pressures by telling them in advance that the flight could be canceled at the last minute due to weather or other reasons" 17. A pilot tells the meeting, the rental desk, and the passengers that the airplane can land somewhere else, or not go at all. For that pilot, a diversion keeps a promise. For the pilot who did not tell them, a diversion breaks a promise. The NTSB named overconfidence at Big Lake and left the 2 hours and 38 minutes on the ground unexplained. The module reads the family's schedule in them, and the Cherokee flew into the hills at Mertzon.