Thursday, April 17, 2008

Nav3, take 2

One week after Nav3 was cut short due to weather, I went with Lee in VH-SPQ to cover the remaining bits, i.e. lost procedures and class D airspace. The plan was to go to Gympie, get me lost somewhere on the way, get unlost, find Gympie, perform a full-stop landing at Maroochydore and get back to Redcliffe.

While going through the Maintenance Release during the pre-flight checks, I noticed that one of the two vacuum pumps was out, which was confirmed by the corresponding light on the annunciator panel during the pre-take off checks. The vacuum gauge was in the green though, indicating that the other vacuum pump was working properly. We would therefore be able to use the two instruments that depend on those engine-driven vacuum pumps, i.e. the artificial horizon (AH) or the directional gyro (DG). And in the unlikely event that the second vacuum pump failed, safety would not be adversely affected since we have back-up solutions for both the AH and the DG.

We do not actually require the AH for VFR flights since we are expected to infer the attitude of the plane from looking at the big natural horizon outside the cockpit rather than the small artificial one inside. My experience so far is that the AH comes in handy for maintaining a given angle of bank in climbing or descending turns, but that’s about it. Of course the AH is a critical piece of equipment for instrument flying or for flying in mountainous areas where no natural horizon is visible. I understand it’s also a welcome help on hazy days or when the sun glare prevents the pilot from clearly distinguishing where the earth meets the sky. But on that day, and for that flight, we could definitely have done without the AH.

Loosing the DG in flight would have been a lot more annoying than the AH, but again no reason to cut the exercise short. Provided it is kept aligned with the compass throughout the flight, the DG helps in maintaining a constant heading with a margin of about one or two degrees. Should the DG fail, we would have had to use the magnetic compass instead. This would be a lot more annoying for two reasons.

First, the compass is a small instrument that is awkward to read. The way to keep a heading with the compass is to turn the plane onto the heading using the compass, pick a feature far ahead of us, use that feature as a reference for flying the heading, and keep choosing new reference features as we move along. Second, the indication given by the compass is only reliable in straight, level and unaccelerated flight. This means no heading information is available during prolonged climbs, i.e. precisely when the nose of the plane covers whatever distant feature we may have decided to use. Flying with only the compass is not impossible of course, many planes do not have a DG at all, such as the Tiger Moth below. But you will also notice that the compass on the Tiger Moth is a lot bigger and probably easier to read than that found on modern light aircrafts.

We took off, left the circuit and tracked north-west to Gympie. Soon after leaving Redcliffe Lee put me under the hood for a while and got me lost somewhere in the Sunshine Coast hinterland.

Getting un-lost was relatively easy. I noted the time, slowed down the airplane and started to fly a racetrack pattern around a nearby township that I chose as my anchor point. Reading “ground to map”, I could see a lake a couple of miles to the east, with a dam at its northern end. This matched Lake Baroon on the map within the circle that contained my most likely position. The only problem was that the map didn’t show any township to the west of the lake. This was really puzzling. Everything else matched: the terrain, the road, the power lines, even a radio mast a bit further to the west. Lee hinted that maybe not all townships are on the map. It all suddenly made sense, I declared us un-lost and we were soon back on track.

We continued on the Gympie, I found the field quite easily and turned right towards the entry point for Maroochydore. I obtained a clearance from the tower who asked me to report sighting traffic going in the opposite direction below me. It took a little while but I eventually spotted the other plane, reported “traffic sighted” and soon after we were cleared for a visual approach to runway 12.

I made a very average landing, vacated the runway, switched to the ground frequency to realise it is actually the same controller as the tower frequency. We taxied to the GA parking, had a bite to eat and something to drink. Lots of helicopters and GA aircrafts around, in addition to jet traffic for Virgin Blue.

We started up again, obtained taxi and airways clearance direct to Redcliffe and taxied to holding point Juliet for runway 12. We taxied by the Maroochydore campus of the Singapore Flying College which trains pilots for Singapore Airlines using a range of GA aircrafts but also a Learjet 45.

Airborne, departure call, identifying Ring Tank then the boundary of the Class D controlled airspace for Maroochydore. We are already within 10 miles of Caloundra, so call to the CTAF and then back to Redcliffe where I made a decent landing this time.

We stopped at the Flinders Aviation workshop so that they could have a look at the vacuum pump and order a new one in. That's when I learnt that, even though they are called left and right pumps on the annunciator panel, they are actually more like top and bottom pumps in reality.

Taxi back to the club, then debrief. Lee said I was ready to go on to Nav4, my first solo nav. This is so cool. Really looking forward to that. Still have to work on maintaining altitude more precisely (read: within a hundred feet), especially in controlled airspace. And maintaining heading too. My departure call out of Maroochydore was sloppy, so I’ll have to improve that too.

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