Nav7: Back to Redcliffe

Before starting up in Goondiwindi for the last leg of Nav7 I didn't forget to turn the GPS logger back on, so this post will be illustrated with the actual track I flew. Hopefully this will compensate for the lack of photos. GPS tracking is the aviation equivalent of reality TV: no details will be spared, and all embarassing navigation mistakes will be exposed.

The plan was to fly from Goondiwindi (YGDI) back to Redcliffe (YRED) via Millmerran (YMMN), Toowoomba (YTWB) and the township of Esk. As can be seen below, I departed Goondiwindi on runway 22, flew a short crosswind leg, turned downwind and kept climbing for an overhead departure.

I could have made my life simpler by departing on downwind rather than overhead since my outbound track was nearly parallel to the downwind leg. Another thing I could have done better would have been to make sure the extended outbound track pointed at the airfield instead of being about one mile to the north of it.

I kept climbing to 5500ft while maintaining a heading of 033 degrees to Millmerran. The track to Millmerran as drawn on the map was actually 041, but given the forecasted westerly winds at 25 knots I had computed before the flight that the nose of the airplane had to be pointed 8 degrees left of track to compensate for the expected drift. The idea was to keep flying the planned heading and check later if I was where I expected to be or if any adjustements had to be made. In a nutshell, that's the navigation technique known as dead reckoning.

About two thirds of the way to Millmerran I could see on the left-hand side a power line oriented north-south crossing a road oriented south-west north-east. From the WAC chart I could easily tell where I was, which was good, except this was not where I was supposed to be!

I was actually about 5 miles north of the track. I had already flown 45 miles from Goondiwindi, with 20 more to go before Millmerran. Maybe the wind was not as strong as forecasted or had assumed a different direction, resulting in my heading over-correcting the expected drift and taking me further to the left of track. Or maybe I misaligned the compass and the DG. Finding why it happened was anyway secondary to fixing the problem.

That's when the navigation technique known as one-in-sixty comes in handy. It is based on the fact that being off track by 1 mile after 60 miles flown means an angular error of 1 degree. 2 miles after 60 miles mean 2 degrees, and so on. It works great, at least for small angles. From a mathematical point of view, this relies on the fact that the function tan(x) can be approximated as x for small values of x. But let's not complicate things, since the beauty of the method is that it can be done in the cockpit while flying.

It goes a little bit like this: I am off track by about 5 miles after about 45 miles flown. Let's say 50 instead of 45 because it makes calculations easier. 5 in 50 is like 6 in 60. So I was over-correcting drift by 6 degrees. If I turn right 6 degrees now, I will fly parallel to my intended track. However, if I do that I will still be 5 miles off-track. So I need another one-in-sixty calculation to determine the closing angle that will take me straight to my destination. I still have 20 miles to run till Millmerran, 5 in 20 is like 15 in 60, so if I add an extra 15 degrees to the 6 degrees found previously, this means I need to turn right 21 degrees to be on a track to Millmerran. New heading is therefore 012.

And it works, as can be seen in the picture above: after turning onto the new heading my new track was pointing at Millmerran. Near Millmerran I went a bit right of track in order to keep the aerodrome on my left, simply out of curiosity. Then I turned onto a new heading and tracked for the Toowoomba aerodrome. I used the drift correction from the one-in-sixty exercise conducted a few minutes before to compute a new heading.

I picked up the ATIS for Oakey on their VOR frequency. The sequence letter for the information was Zulu, meaning the military control zone was not active and had reverted to a CTAF. My track only clipped the CTR by a mile or so, but I would nevertheless have needed to request a clearance if it had been active. No need to upset the military. I prefer to see fighter jets and big black helicopters at airshows rather than at the end of my left wingtip.

Toowoomba is blessed with an NDB navaid, so I tuned it in and the needle on the ADF was pointing straight ahead. The ADF needle points at the navaid in relation to the airframe, not in relation to the track as is the case with VOR navaids, so one has to take drift into account. However, since I was no longer offsetting a lot of drift, the nose of the airplane was pretty much pointing where the airplane was going, and therefore the needle pointing straight ahead was good news.

I made a couple of calls on the Toowoomba CTAF to let everyone know I was intending to overfly the field at 5500ft. At this altitude I couldn't really have conflicted with traffic in the circuit, but it's good practice. The GPS logger can be cold and cruel at times, pointing mistakes that would otherwise go unnoticed, but in the present case I'm happy to report that my track took me right overhead the airfield.

After Toowoomba I tracked for Esk. Under my left wing were the Cressbrook and Perseverance Creek reservoirs that I had overflown on Nav3 six months ago on my way to Oakey. The hilly scenery was really beautiful in the low light near the end of this winter afternoon. I found Esk and confirmed it with Mount Esk, the racetrack and the red rooves of the Esk Hospital. I descended to 3500ft and once clear of the ranges kept descending to 1500ft to remain under the CTA steps of Brisbane International. 

The GPS logger got its revenge when I joined the circuit at Redcliffe. I was coming in from the west at 1500ft and my track was taking me straight to the airfield. I turned right a little so as to be on the south side of the extended centerline for runway 07/25.

The dead side at Redcliffe is always to the south because all circuits are over the water, i.e. left-hand circuits for 07 and right-hand circuits for 25. That's both for reasons of not overflying populated areas, and avoiding any controlled airspace violation. The Brisbane CTA step over the Redcliffe aerodrome is at 1500ft, and there's a 1000ft step just a couple of miles south of the field.

I knew from listening to the CTAF frequency that runway 07 was in use, which I confirmed by looking at the windsock as I was descending to circuit height over the dead side. The winds had changed since earlier in the day when I took off on 25.

I joined crosswind above the opposite end of the runway. I turned downwind a bit too early so I widened the leg a bit. This is why the track does not look anything like the nice figures in flying training books. I landed on 07, taxied out and refuelled the airplane. I cancelled SARTIME by phone then sat down a few minutes to jot down some notes about the flight so that I could blog about it later. Total flying time today 4.3 hours, at $185 an hour plus $29 for landing at Archerfield. Oops. Looking forward to being able to take passengers with me to share the cost.

So that's it. The navigation part of the PPL is now over. It's a bit of a weird feeling. Next step, PPL pre-test and then test. And hopefully many more adventures after that. And I need to blog about the CSU endorsement. And the PPL theory test. And the airshow in Singapore. And write a guest post for Plastic Pilot. Too many blog topics, not enough time.

Nav7: Things get windy in Goondiwindi

I landed at Goondiwindi at the conclusion of the second leg of Nav7 with an empty water bottle and a correlatively full bladder. Note to self: get smarter with water intake on long legs. After shutting down the engine and securing the airplane my first objective was to locate a bathroom. Any bathroom for that matter.

From a distance I thought the building in the picture below was someone's house. I was ready to knock on the door and beg for the use of those kind people's lieux d'aisance when I realised this was actually the terminal building.

The building was empty but I could still access the facilities. There was a small waiting room with retro-styled lounge chairs, a few leaflets for local businesses and attractions, and a Bible. A sign on the bathroom door was advertising local joy flights conducted by Sudholz Air Charters, a charter company based in Goondiwindi which operates a Piper Saratoga and a Cessna Crusader.

The McIntyre Aero Club is housed in the same building and a plaque reminds visitors that it is Sir Joh Bjelke-Petersen who officially opened the club house in 1991, just like he did with the Barambah District Aero Club in Wondai which I visited on Nav1 and again on Nav4.

Interestingly, at least to spelling sticklers like me, his last name is spelled Peterson here, and not Petersen as it should be. I wonder if Sir Joh noticed the typo when he unveiled the plaque in 1991. My guess is that he didn't: this was the year the former Queensland Premier faced a criminal trial for perjury in relation to a large corruption scandal known as the Fitzgerald Enquiry so it's fair to assume he had more pressing worries on his mind.

There wasn't anyone around at the aero club, but they must be a nice bunch of people, given that they organise breakfast fly-ins to coincide with the Gourmet in Gundy wine, food and art festival. And of course they have a brick barbecue on the front lawn.

I had my sandwich on the nicely flowered front deck before proceeding to the back of the building.

All three motels in town offer a courtesy pick-up service from the airport. I hope they also give free rides back to the airport in the morning.

And if you're not heading for a local motel you have a choice of two local cab companies. The Gundy Cab Co. uses a six-digit phone number that takes us back to the previous century. Someone wrote "put correct phone number here" on the other sign advertising the Cotton Country Cabs, but I don't think this would be enough: the business is actually up for sale.

The tour of the aerodrome wouldn't be complete without mentioning the weather station.

The circular device in the foreground is the evaporimeter. Wind speeds and direction are measured at the top of the pole on the right, while the white box on the left measures all other parameters such as temperature, humidity and dewpoint temperature.

I walked back to the apron to check out the only two other planes parked there: a Cessna Crusader and a Cessna 182. So with our C172 that was a bit of a Cessna family reunion.

The Crusader is a six-seat twin-engined airplane with counterrotating propellers, i.e. one propeller turns clockwise while the other turns anticlockwise. This makes the mechanical design and maintenance of the airplane harder, but on the other hand avoids having one engine labeled as the critical engine, thereby improving handling in case of failure of the critical engine.

I went back to VH-SPP to prepare everything for the next leg. The wind had picked up since I landed and turned very gusty. I was surprised because gusty winds were forecasted for aerodromes further north such as Oakey (15 knots gusting at 25) and Toowoomba (16 knots gusting 26), but not for Goondiwindi where the forecast was 14 knots with no gusts.

On the synoptic below Goondiwindi is near the top of the black arrow that says 35 knots, right in-between the cold front and the trough on the east coast of Australia. For those readers more familiar with how things work in the Northern Hemisphere, keep in mind that in the Southern Hemisphere winds rotate clockwise around a low and anti-clockwise around a high.

The wind was actually so gusty I could feel the plane rock from side to side. I was getting worried that I would not be able to take-off safely. The good thing though was that the wind was less than 30 degrees off the runway direction, so I knew I could handle the crosswind component, it's the gusts in the headwind component I was worried about: what if I rotated in a gust, lifted off and then got robbed of 10 or 15 knots of headwind? This would bring me very close to stalling speed. 

I taxied to the run-up bay, did my pre-take off checks, entered the runway and backtracked. From where I was I could see the windsock quite well. The plane was still rocking a bit from side to side with the gusts. I put ailerons into the wind, full power and kept some forward pressure on the yoke to make sure the airplane would not take-off prematurely. At 65 knots airspeed I started rotating and the airplane lifted off quickly and nicely into the blue sky for the last leg of the trip.

And apologies for the corny title. I couldn't resist.

Nav7: from Archerfield to Goondiwindi

Soon after taking off from runway 28L I left the controlled airspace of Archerfield aerodrome, on my way to Goondiwindi. This marked the start of second leg of Nav7. The first one was recounted here. The last words I heard from the tower controller were "cleared for take off 28L". No notification of leaving controlled airspace, no "frequency change approved" and no requirement to make an airborne report either. That's because Archerfield is a GAAP airport, an idiosyncrasy of the Australian airspace system. A GAAP airport is a non-radar towered airport with simplified procedures designed to catter for high-density General Aviation traffic. And there's no taxi clearance either.

I was now in Class G airspace, but only a few minutes away from entering the Class C controlled airspace of the Amberley RAAF base. Most week-ends this airspace is de-active and reverts to Class G airspace where CTAF rules apply. It's just like any other non-towered aerodrome, just with much much longer and wider runways. The airspace however can become active on very short notice. The consequences of busting controlled airspace, and especially military controlled airspace being dire, I double-checked the status.

I tried to get the status from the Amberley ATIS on the NDB frequency but I couldn't hear much of the recorded voice message over the morse code and the static. So I called Brisbane radar and requested the status of Amberley, which the controller said was de-active. Good. That meant I could track direct to Gatton at 2500ft instead of having to request a clearance and possibly being told to go the long way around the aerodrome via the westbound VFR route. 

I identified the Goodna VFR entry point for Archerfield on my left and kept my eyes out for any incoming traffic. I could already see Ipswich, the Amberley aerodrome and the Swanbank Power House. I kept listening to the CTAF frequency for Amberley and made a few position reports. There was only one other plane on the frequency, a Cessna 172 doing circuits at Amberley. I could now see the township of Marburg right ahead of me in the foothills of the Mt Grandchester range. I climbed to 4500ft and found some light turbulences, a harbinger of things to come.

I kept tracking west to Gatton, which was easy to identify thanks to Lake Clarendon to the north and the highway and the railway both running west. I turned south and started climbing to 8500ft. I had initially planned to stay at 6500ft but later decided to buy myself a bit more safety and gliding distance in the event of an engine failure. 2000ft extra mean about 3 more minutes at the descent rate obtained for the best glide airspeed of 68 knots, which in turn means about 3 extra nautical miles in the glide. Over a mountain range with peaks at 3700ft, this could make  the difference between landing in a paddock in one of the valleys below or having no other place to land than a heavily timbered area on a mountain slope. Did I mention that one of the highest peaks in this area is named Mt Mistake, at 3582ft?

Turbulences were present throughout the climb but ceased suddenly as I passed 7000ft. It must have been the altitude where the temperature inversion was sitting and prevented air heated up by contact with the ground from rising any higher. My best guess is that this was a subsidence inversion caused by the air being pushed downward in a high pressure system and warmed up by adiabatic compression before spreading out parallel to the ground. Yes, I've been reading the CPL Meteorology book recently in preparation for the PPL Theory exam. Anyway, whatever the reason, the visibility above the inversion was just amazing. I could see all the way to Clifton, about 30 nautical miles away.

I was far from any CTAF so I was listening to the area frequency, which was very quiet on this Sunday afternoon. There was a lot of static though, and I couldn't make it go away by using the squelch knob. I made sure the radio was not in the test position which bypasses the squelch. I was tempted to turn the volume down but then I couldn't hear what was being said on the frequency, which is bad airmanship. Then suddenly it dawned on me. I tried using the COM2 radio instead of COM1 and the problem disappeared.

The air coming into the cabin through the ventilation duct started to get a bit colder, reminding me of the temperature when I left home earlier that day. The Outside Air Temperature (OAT) gauge indicated only 2 degrees C. That's the LCD display in the top-left corner of the instrument panel, left from the airspeed indicator. With the rule of thumb of loosing about 2 degrees per 1000ft, this was consistent with a ground temperature of about 20 degrees.

Approaching Warwick I gave a call to the CTAF, even though at this altitude I couldn't interfere with traffic in the pattern. Better safe than sorry. Over Warwick I turned right and started tracking to the south-west and Goondiwindi via Inglewood. 

Lake Leslie appeared just a few miles to my left. I looked at my map and realised the planned track was supposed to take me right over the lake. I was offtrack to the north by a few miles. I did a one-in-sixty calculation which gave me a new heading for Inglewood. By the time I had finished the calculation and turned onto the revised heading I could already see Inglewood in the distance, more than 20 miles away. Damn visibility. Makes dead reckoning navigation too easy, as Australians like to say.

I tried not to look at the GPS at all on this nav, but I still had it on just in case. I had a quick glance. My groundspeed was 81 knots. My true airspeed was around 115 knots, so that's a headwind component of 35 knots, a lot more than the forecasted 25 knots. The problem was that fuel planning in Nav7 is critical. If I had taken off from Redcliffe with full tanks, I would have had barely enough fuel to complete the flight within the legal limits. That's why I refuelled in Archerfield, which increased my fuel margin by 11 litres, or 16 minutes in the air. Now the increased headwind was robbing me of my fuel margin. Not good.

I decided to descent to 6500ft hoping that the winds were weaker there. They indeed were, and my groundspeed increased to 97 knots, 16 knots more than what I was doing 2000ft higher. The increased groundspeed came at a price though. I had crossed the 7000ft level where turbulences had stopped on climb, and they came back with a vengeance on descent. It was very very bumpy. It was like someone was slapping the airplane from the outside. Maintaining altitude within a hundred feet of 6500ft required all my attention and I was not terribly successful at that. I decided to stay at this level anyway since I only had about 20 miles to run before starting my descent into Goondiwindi.

I found the aerodrome right where I expected it, although later than expected. Maybe I should have delayed my descent a little, which would have given me a steeper descent angle and therefore a better view of the area. The fact that the runway 04/22 was nearly parallel with my track of 247 degrees didn't help spot the runway early either.

No-one could be heard on the CTAF frequency. I overflew the runway, looked at the windsock which was favoring runway 22 with a strong crosswind from the right. I joined the circuit and made a descent crosswind landing on this sealed runway. When I turned on final I was surprised by how narrow the runway looked. I looked it up later and realised it is the exact same width as the runway I am used to at Redcliffe. Only that it is double the length, hence the optical illusion that it is narrower. I had just experienced a textbook optical illusion.

I taxied to the apron, chose a parking spot not too far from the terminal and shut down. I tiddied up the airplane only to found that my empty water bottle had halved in size since I last drank from it at 8500ft. The elevation at Goondiwindi is 714 feet, which means the atmospheric pressure is about 250 hPa higher than at 8500ft, an increase of one-third. One more practical experience that confirms what the book says. One thing I love about aviation is that science is never far if one knows where to look.