Heading, distance, time,
MEF and fuel are great,
Tell someone you'll be late.
Today's lesson was diversions. Again, the weather was clear and cold, not a cloud in the sky, a wonderful day for flying. Especially since I was going to be busy in the cockpit, and turbulence doesn't help.
The Why:
A diversion is when you change your mind mid-way through a cross-country flight (or any flight from here to there) regarding your destination. Reasons might include weather (where did those clouds come from?), fuel issues (man, those are ugly headwinds), passenger illness, or maybe you just changed your mind (the burgers at xxx are yucky, let's go to yyy instead).
The Wrinkle:
When performing the diversion the pilot does not have the benefit of advance planning. Of course, before the flight alternative aerodromes are identified. However, the calculations (time, distance, headings, etc.) are not calculated before the flight. When the decision to divert is made, it's calculating and planning time.
Resources:
Because the pilot has to fly the plane as well as plan the diversion, in the cramped confines of the cockpit, and plan under a time constraint, there isn't time to use rulers, protractors or calculators. The planning will be a "back-of-an-envelope" exercise using estimates, not tools.
Focus On:
- Don't get lost - we're going to be flying a course based on the DG or the compass (magnetic north), but the map's grid lines are oriented on true north. Using a VOR compass rose, or making an estimate using the grid lines and the local magnetic variation, can be used to determine the magnetic heading.
- Safety - In each grid of the map there is a number, the MEF or Maximum Elevation Figure, which is the ASL height of the highest terrain or obstruction (towers, antenna, etc) in that grid. To this figure must be added the required obstruction clearance, for safe flight through that grid. As a specific example, if the reason for the diversion is a descending cloud base, calculating a safe transit to the alternate destination requires priority in the planning.
Planning Procedure:
Circle, circle, line
- Choose, and circle, a Set Heading Point for the start of the diversion.
- Circle the destination
- Draw a line between the SHP and the destination.
- Circle any obstructions along the route.
- Select way points along the route.
- Mark the halfway point along the line.
- Estimate the magnetic heading to be flown.
- Estimate the length of each segment. Since we can't use a ruler, use what is hand (my thumb is 6 nautical miles wide). Some books suggest using a tool such as a notched pencil - the Transport Canada won't allow them during the flight exam.
- Using the current indicated airspeed, calculate the duration of the first flight segment, and the duration of the diversion.
- Check the MEF on the chart, and chose an altitude for the flight. If you can fly at altitude, remember to comply with the VFR altitude requirements (e.g. 4500' for westerly course, 3500' for easterly).
- Knowing the estimated duration of the diversion, is there sufficient fuel. If you can look up the fuel burn in the POH good, otherwise use a conservative estimate. Remember to include the VFR 30 minute reserve (45 minutes for night).
- Fly to the SHP. Record the time at the SHP, and calculate the ETA at the destination.
- Call up FSS (126.7), and amend the flight plan.
- DG is aligned with the compass
- The aircraft should be at the chosen altitude, selected power, and trimmed.
- The aircraft should be on heading
- A cockpit check (temperature, pressures, mixture, etc) is completed.
After the briefing, we launched and flew two diversions. We flew at low altitude, so there was limited opportunity to look far into the distance and say "we're going there" and then just point the airplane.
And I greased the landing when we went home. It happens.
Time: 0.8 dual
After refueling the aircraft and catching up with my instructor inside, he notified me that I had been signed off to fly the Pembroke cross-country route solo.
2 comments:
That's a great summary of Ex 23D (the diversion).
Coincidentally I was orbiting Quyon in a C-172 on Sunday afternoon doing the same exercise. My student flew there from Rockliffe under the hood. After he sorted out where we were, he diverted to Arnprior, where we did a T&G before returning to Rockliffe.
We had to get the aircraft back for the next rental (which started at 10am), and had just headed south from Fitzroy Harbour towards CYRP when we heard your radio call.
Once again, we were int he air at the same time. One of these days we should do it in the same aircraft.
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