The classic divert problem given to students prepping for checkrides runs something like this. The instructor or examiner interrupts an otherwise smooth flight with a simulated condition. "Let's say the airfield we have filed to suddenly is closed because of an emergency." The closure could be caused by severe weather, a mishap, or a chemical spill on the nearby interstate, but for some reason, the original destination is no longer in the picture. It is necessary to quickly replan the flight to a new destination and take positive steps to adjust to the new circumstances.
When assigning a student an in-flight diversion, a flight instructor might expect the new pilot to grab his sectional and unravel it while aircraft control deteriorates. Likewise, the meticulous en-route computations quickly go kaput, as the diversion wild card is thrown in. These easy steps should help to minimize the initial confusion and enable students to approach the problem with discipline and pragmatism.
First, find it. Sectional charts are better used in small, manageable portions than spread all over the cockpit. The proposed diversion airfield is usually not that far away from the originally planned route, so there is no need to look in the next state. Assuming that the student has not identified any divert fields in advance, he should first find the proposed new destination on the sectional and positively identify it. Equally important is knowing the airplane's present position before starting the divert. The pilot should have a pretty good idea of where he or she is. A good technique is to mark present position and note the time. That establishes a known position with a time and leads us to the next step; fix it.
The course line from present position to the divert destination can be drawn with a small plotter, a short ruler, or any straight edge. I prefer the six-inch aviation rulers with nautical-mile scales. They seem to be the perfect size for the cockpit and easily fit into a pocket or checklist page. Once a course line is drawn, measure a magnetic heading on the nearest navaid compass rose, so that the need to convert from true course to magnetic is eliminated. At this point it may also be helpful to further identify the divert field with a radial/DME fix off a nearby station. Now that we have found the new field and fixed it, it is necessary to track toward the divert location.
After the initial map work is done, turn the aircraft toward the new destination and fly toward the divert field while additional computations are accomplished. If the last known position wasn't a sure thing, updates can be accomplished by additional radial/DME fixes or pilotage. If fuel is a consideration, consider a more optimum cruise speed or altitude. Once you are on your way, the work is not done - you must time the divert procedure.
Time is a critical element of the navigational triumvirate - distance, rate, and time. From our previous steps, we should have an initial heading, a course line, and, through measurement, a distance to the divert location. Once we have a reasonably accurate mileage, we can apply our estimated groundspeed and come up with a time to fly. With the time and pilot's operating handbook knowledge of the fuel consumption rate, we can also determine how much fuel will be required. These are standard E6B flight-computer calculations.
While cruising to the divert field, a pilot can improve his posture for arrival with a little additional effort. There are the usual in-flight resources available for weather updates (FSS, AWOS, etc.), but knowing a little about the field would remove much of the uncertainty. Although the ideal solution would be to pull out an Airport/Facilities Directory and get the airfield layout, the sectional airfield information provides a good layout too. From the chart the pilot can read runway length, the common traffic advisory frequency, and field elevation. From the basic information, the student can determine an approximate pattern altitude by adding 800 to 1,000 feet to the field elevation. Likewise, the direction of traffic can be determined (left-hand traffic unless "rp" indicates right traffic on the sectional).
The steps outlined in F2T2 don't guarantee success but they do give an easy method to remember procedural approach to diversion. By using the find, fix, track, and time methodology, a pilot can proceed from an old position and course line to a new one with a minimum of confusion. The goal is to proceed to the new destination with minimum disruption. The same old principles of time and heading still apply, and sound airmanship is still required to successfully complete the divert.
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