Squaring the Circle

Task-saturation can distract us from flying the aeroplane. At the worst possible moment.

My student Denis was doing so well on this final check flight, a few days before his official instrument rating skill test. We had completed a comprehensive oral session on the ground, and his knowledge of the required theoretical aspects of instrument flying was excellent. A detailed preflight briefing followed, after which we headed out to the skies. Denis had by now flown nearly all the required routes, manoeuvres, procedures and approaches as per the test regulations. He had “aced” them, performing well above the minimum standards required. There was just one item remaining - to fly an asymmetric (i.e. with one engine simulated, by reducing its power, as having failed) approach to landing. Our plan was to do this from a circling manoeuvre, noted on the charts as a "Circle-to-land".

Such approaches are not always required in skill tests. Recognising that air traffic control requirements, weather, or other factors on a given day may preclude them, official guidance says the asymmetric approach to land in the skill test will “generally” be flown from a circling approach. But it is good teaching practice to expose the trainee to anything that might be asked of him or her in a test, or for that matter in later operations. On this breezy morning air traffic control were willing to oblige. We had previously flown a similar approach at a different airport in calm conditions, and had tackled this particular procedure in the “sim” a few times. Denis had always managed them well. But the sim is not the real world, as we were soon to be reminded.

So what exactly is a circling approach? It is a procedure whereby an aircraft is initially flown and descended towards a particular runway by flying an instrument approach, but is then manoeuvred visually, once the required visual references have been obtained, to land on a different runway at the same airport. This might be done for various reasons. For instance out-of-limit winds, or work in progress, on the instrument runway itself, or a failure of landing guidance equipment on the intended landing runway. If weather is close to minimums, it might entail your emerging from cloud as low as 500 feet above ground level, with visibility of as little as 1500 metres. Then you enter what is effectively a low-level circuit, keeping the intended runway in sight, to position the aircraft safely for a stabilised final approach. You’re low, slow, and turning - the notorious threat-filled profile, potentially deadly unless flown with impeccable technique and attention to what you’re doing. All the more, so in reduced visibility or a lowering cloudbase. Worse if your thrust is no longer symmetrical, as we were practicing today.

In other words, it’s demanding. So much so, that numerous commercial operators prohibit circling approaches entirely. Others require significantly increased minima or special training, or approval for specific airports. The statistics explain these policies quite starkly. A 2011 study by Flight Safety Foundation reported that “controlled flight into terrain (CFIT) studies have shown that runway aligned approaches (Lateral Navigation only) are some 25 times safer than circling approaches and that once some form of vertical guidance is added to these, then the safety margin is increased again by some 8 times”. Putting the figures bluntly, a circling approach can be 200 times less safe than a precision approach such as an ILS!

Nonetheless, here we were, preparing to conduct a circle-to-land. Denis briefed the approach very thoroughly, and I listened intently, to be certain we both had the same situational picture, or “mental model” of the procedure in our minds. The plan was initially to fly the ILS (instrument landing system) approach towards the southwesterly-oriented single runway, and then, once visual, to circle the airport and land on the same runway, into wind, in the reciprocal direction. I was cognisant of the paradoxical situation whereby training can frequently carry more risk than normal operations. The reason being, that in order to train for and assess competence in the manoeuvre, we were going to fly down to the published minima in simulated instrument meteorological conditions. The IMC would be simulated, but our proximity to terrain would be all too real. Whereas, in routine operations, if we became visual with the airport at a higher level we would certainly have flown well above the official minima if conditions permitted, affording us a greater vertical distance from terrain, and accordingly a much improved margin of safety.

Mentally prepared, and cleared by ATC, Denis commenced flying the ILS approach, appropriately trimmed and configured with our one “working” engine. An additional factor that made the approach different from normal was the strong tail wind component. Generally, of course, we fly approaches into the wind, but in circling you’ll often have the wind behind you while on the ILS or other instrument procedure. This meant that even though flying the correct target airspeed, our groundspeed was significantly faster than usual. That in turn necessitated a greater descent rate than normal in order to maintain the glide slope gradient. Denis’s body language told me he was working at the height of his concentration in order to stay in the groove, keep the needles centred and stay on speed. Another complication was that the wind wasn’t directly behind us. It was quartering from the north, so an additional cross wind component was at the same time trying to push us to the left, and Denis was countering by pointing the nose a few degrees to the right, working within the directional “bug” to stay straight on the localiser beam as the wind’s strength varied with the decreasing altitude and the effects of terrain. Still, with his intense focus, he kept us on the required flight path with admirable accuracy. In a few short minutes we levelled off just above our minimum circling altitude and he announced to ATC we were visual with the airfield.

The controller then threw in a wild card: he offered a choice of either a left or right downwind for the opposite direction runway, at pilot’s discretion. I was tempted to jump in with my own response, but this was a test, and I let Denis make what I recognised, immediately, was the wrong decision. He opted to join a left downwind, and turned about 30 degrees to the right in order to join it. It’s the direction many pilots instinctively choose if occupying the left-hand seat, for the simple reason that it is easier to keep the runway in sight while looking out of the window on that side. The problem on this day, however, was our quartering tail wind. Not only was it pushing us at a greater groundspeed along the downwind, it was also pushing us towards the runway, and Denis, preocccupied with pre-landing checks, wasn’t doing enough to counteract that. Worse, when we turned on to the base leg, our cross wind was to become a tail wind. That would seriously shorten the amount of time available on base, and it would also increase the turning radius required to roll out, correctly aligned, on our final approach.

The interesting thing was, we had discussed this specific threat in the preflight brief, and we had also explored it in some detail previously in the sim. Alas, all that was forgotten in Denis’s efforts to maintain the correct speed and altitude, and to keep the field in sight while liaising with ATC. He commenced the final turn too late. At the shallow bank angle dictated by our single engine configuration, sure enough, we shot through the extended centre line to the far side, and it was clear to me we could not safely recover to a stabilised approach. Denis had other ideas, however, and he started to bank our craft beyond the maximum permitted angle in these circumstances, only to be halted by my immediate grasp of the wheel and my peremptory command “Negative, GO AROUND!” Shaking his head in annoyance with himself, Denis gathered his thoughts and conducted the go-around correctly. He retrieved some brownie points by remembering that the missed approach procedure was the one for the instrument runway, not the landing runway. He was getting tired at this stage and we flew around the field once more conduct a successful “normal” single-engine approach to land.

During our debrief he told me that having put in such a huge effort to fly this demanding procedure, he was determined to get the aeroplane on to the runway. He wanted to enjoy the “success” of completing the approach, and that was what had urged him to attempt the potentially dangerous steeper turn (on one engine, close to the ground!) in his attempt to align us correctly on final. Even while doing so, he said, “a voice in my head was telling me this was all wrong”. But the effects of task-saturation, together with a large dose of get-there-itis, had overcome his better judgement. Denis’s experience was a perfect example of how an exemplary flight can be endangered, at the very last moment, by a crucial lapse of judgement. In analysing the event we agreed that a more detailed approach brief should have included the likely effects of wind on the base leg. That might have prompted him to fly downwind, when offered the choice, on the opposite side. The margin of time and space thus provided would have been a safer asset than the convenient view out of the left side window. Sometimes you have to select the better option, not what seems to be the best one. He also suggested that if he had voiced the permitted bank angle limit during the briefing, it would likely have inhibited him from trying to yank our craft to where, unsafely, for a crazed moment, he wanted to take it.

As we adjourned for a coffee, he reminded me of “three golden rules” I had exhorted him to follow, early in his training, no matter how distracting the onslaught of tasks has become: “1. Fly the aeroplane. 2. Fly the aeroplane. 3. Fly the aeroplane”.

A couple of days later, Denis passed his final instrument rating test with distinction. A circle-to-land wasn't required, but I am certain he would have flown it perfectly if asked.

A version of this article was first published in Flight Training News

A few other meditations on the joys of pilot training can be found here