Crowded circuit flying over Cambridge

After my last hopeful post in March, it was another couple of months of bad weather, but a few weeks ago when the weather changed, it was good enough to make two flights in one day. It was a pretty challenging day, with a lot of other traffic in the circuit, and a few more reasons for it to be challenging.
One of the hard things about flying in the circuit is simply your workload. All the things you have to do are individually quite simple (apart from the landing itself), but you have to do them all in a limited time, one after another without pause. When you're a student pilot, and you have to concentrate even on the easy things, you're always on the edge of having too much to do. Any extra work can send you over the edge, and things start to go wrong. That's why we have to practise!

You might expect that the first day of good flying weather would be very busy, and you'd be right. There was a lot of traffic this day, and it definitely increased my workload. The circuit pattern is like a queue, and you have to keep your place in the queue, behind other aircraft. This wouldn't be hard, but (a) all the aircraft want to go at different speeds, (b) different pilots tend to turn the legs of their circuit in slightly different places, mainly because aircraft have different climb and descent rates, (c) in the Tiger Moth, you can't see directly in front of you, so you want to make sure the aircraft in front is a leg ahead of you, and (d) if the queue gets held up, you can't just stop behind the one in front.
Although you can't just stop, you can fly in circles, or orbit. If there isn't enough separation between aircraft, the controller might ask the trailing one for "one left orbit at start of downwind". This happened to me quite a lot.
This seriously increases workload because you have to be a lot more responsive. You spend more time listening and talking on the radio, and you might have to adapt what you're doing as instructions come in. Sometimes it feels like a game of Simon Says. While you're orbiting, you have to be careful to keep the circles neat and over the same point on the ground - probably while the wind is blowing you in one direction. You might have to change the shape of your circuit in other ways, such as making a longer downwind leg to be sure you stay behind another aircraft.
Worse yet is when there is an aircraft flying on instruments. Instrument traffic doesn't use the circuit like visual traffic. Instead, their correct course is between certain radionavigation beacons. Each runway at each aerodrome has a published instrument approach, which the aircraft has to follow. This means that they don't join the same circuit as the rest of us, and typically the last few miles of the approach are flown straight towards the runway. This holds up all of the visual traffic, because the controller needs to be sure the approach has no other traffic on it, before they can clear the instrument traffic for final approach.
On this day, it was obvious right from the start that instrument traffic would cause hold-ups for the visual traffic. If you've been reading this blog a while, you know that I have to cross the main runway to get to the parallel grass runway. The grass runway is almost exclusively used by Tiger Moths, and has no instrument landing equipment; most traffic and all instrument traffic uses the main runway. When I called for taxi out to the grass runway, I was only cleared as far as holding point J, holding short of the main runway. I had to sit there with the engine running for nearly ten minutes while we waited for a Boeing 737 to make an instrument approach and land on the main runway.
Even once we were airborne, the traffic still made things harder for me. On one circuit I was instructed to "make right orbits until advised". It was quite a windy day that day, and every time my orbit crossed the wind direction it blew the aircraft out of balance and the cobwebs out of my ears. I was constantly fighting to keep the turn stable and co-ordinated. It was very draining and by the time we were instructed to roll out and continue our circuit, I was dizzy and worn out.

Contributing to that fatigue were some unexpected procedural changes. Conventionally, after take-off you continue to climb and fly straight ahead in the runway direction, until you pass the aerodrome boundary and reach 500 feet of height (whichever is later). After that, you make a 90° turn and continue climbing until you reach 1000 feet.
Lately, the chief flying instructor (CFI) at the Group has had a bee in his bonnet about taking off from runway 23. The climb-out is over a built-up part of the city with no fields ahead. If the take-off run is long (which sometimes it is, especially with student pilots like me), you don't have a lot of height when you get over the built-up area, and he's concerned that it would make it very hard to land safely in the event of an engine failure.
For this reason, he's been encouraging pilots to start their turn early: as soon as they cross the aerodrome boundary. Just 30° to the left puts the farmland in the south within reach. That said, starting that turn early really hurts the Tiger Moth's rate of climb, so it seems to me like it's exacerbating the problem as much as it's easing the risk.
Although we hadn't briefed that we would do this, as soon as we'd crossed above the aerodrome fence, he told me to start my left turn onto downwind immediately. He didn't even let me know at first how far we'd be turning initially, and having to react to his instructions definitely added to my workload at that sensitive time.

That wasn't the most exciting part of the flight, though. One of the aircraft you can learn on at Cambridge is an Extra 200, operated by our neighbours at Cambridge Aero Club. It had been doing some upper air work, and it wanted to re-enter the circuit. Because they were already over the aerodrome, the tower offered them to join by integrating into the downwind leg directly. From above us, they would descend to circuit height (1000 ft) in front of us. Integrating from above like this can be quite dangerous, especially for an aircraft like the Extra where you can't see below your nose, and it's very easy to descend right into another aircraft. It's especially bad when you can't see upwards out of the Tiger Moth (because of the fuel tank and upper mainplane).
Extra 200, but not the same one. Photo courtesy Wikipedia Commons user Huhu Uet [GFDL ( or CC BY-SA 3.0 (]
Because of this, after we were warned by the tower that the Extra would be descending ahead of us, we elected to slow down to 65 mph: about half its speed. As you might remember from my lesson on slow flight, flying at 65 mph requires a lot more concentration, and we had to maintain that speed for almost the whole downwind leg. Even with these precautions, and warned to look out for it, I never saw the Extra descending in front of us, until after it had turned the corner onto base leg.

I've often said that we're spoiled in Cambridge by being able to learn procedures at an airport with a very professional ATC that's used to dealing with larger aircraft and plenty of traffic. But the cost of that is that sometimes we have to deal with the larger aircraft and heavy traffic too! It keeps you very busy, especially when you're spending all of your flight time in the circuit, and you're trying to learn the skill of landing too.

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