27 August 2012

Basic Instinct

It was an evening sortie, long-haul, to FSO Perintis and thence to Angsi A. The haze clung insistently to the restless sea, and the winds could not beat back the unwholesome air that hung over all, airman and sea man alike.
The Captain wanted to fly out, so I contended with the flight log, recording the range calls and fuel consumption as we left the shoreline receding behind us. The first 40 miles out to sea were uneventful, the writing and radio calls all being boringly regular. Within those 40 miles the navigational reference was the radio beacon radials from Kerteh, and the autopilot flew us accurately away headed out towards FSO Perintis. The miles increased predictably till we reached the 40-mile Kerteh Zone Boundary limit, from whence we would be reporting solely to Heli Base Kerteh, and navigational data would be by reference to GPS.

I made my radio calls, whilst the Captain switched the aircraft autopilot to track the GPS path to Perintis. Monitoring the navigation displays, I saw that all was in predictable order, even with strong winds from our 7 o'clock. To depict this, first of all, the glass cockpit displays would normally show the straightline GPS track heading to the destination, and normally the track line would coincide with the heading marker positioned on the 12 o'clock spot on the compass rose, from which we pilots reassure ourselves that we are on the correct heading to the destination. With some wind from either left or right, there are times when the track line would appear drifted but the heading marker would stay at 12 o'clock, telling us that the autopilot has corrected and compensated for the wind drift and that the current heading would allow the wind to drift us over the remaining distance to make good our arrival overhead the destination. In other words, while the wind may be blowing us downwind, the autopilot is flying us further into wind so we eventually end up right over the destination.

At the 40-mile mark, I noticed that the GPS prompt said GPS NAV 1 LOST. Yeah, okay, that happens quite often on GPS NAV 2. Not being able to rely on the coordinates I selected on Leg 1 as the GPS was no longer resolving that leg, I thought to select the same coordinates on the Leg 2 instead. And then as fate would have it, hardly a minute after confirming Leg 2 coordinates as the autopilot reference, the annunciator prompted us that GPS NAV 2 LOST. Then we both saw something unexpected on the navigation display. The entire track line jumped about five miles left, the way an image jumps on astro transmissions in the middle of a menagerial thunderstorm. This led to the autopilot making a severe bank to the left to regain track correction and minimise the track error within wind drift limits. This was because the GPS was now working in memory and dead reckoning mode, and the autopilot was merely obeying the command to stay true to the now guessing-game mode on the GPS. We noticed that the GPS location diamond for Perintis did not coincide with what we perceived as the weather radar echo blimp painting her position.

Not wanting to have a bad Hollywood moment with the passengers over an easily remediable situation with a repeat of sudden autopilot inputs, GPS autopilot coupling was disengaged and the autopilot was coupled to the selected magnetic heading of the aircraft instead.

On any clear day, this would have been peanuts. But on a haze-choked day, with poor visibility, identifying the destination ship became a bit more insistent on basic navigational practise as was done before the days of GPS. This meant that we would have to return to tracking towards the destination by homing devices, such as the ship's non-directional radio beacon.

Many a time, rigs and ships have not switched on their beacons over many reasons, none of which I have plumbed, although it remains an operational requirement on the part of the destination rig or ship to switch on the beacon when an aircraft is bound its way. With the acclimatisation to sophistication and automation, the reliance on GPS autopilot coupling has turned out to be the order of the day. Simply put, we can easily take secondary navigational devices for granted when we are used to the friendliness of GPS autopilot coupling. The software glitch that occured this interesting evening of the 25th of August was valuable in showing us how no matter the impression made by the level of sophistication on an aircraft, basics will always be what makes us aviators first and systems managers second.

Safe on the deck of FSO Perintis

And so, the Captain and I spoke with the radio operator of FSO Perintis to keep the beacon on. An NDB test was done to ensure that the instrument needle was actually tracking the beacon, while the Captain dead reckoned the general direction of Perintis by interpolation when we overflew Sotong Collector. It was interesting to see, though, that in haze and the featureless sea, dead reckoned navigation did not inspire confidence, as every single degree of inaccuracy would cost us fuel, and would require a decision should the destination not be found in time. In the haze, many things could appear as an FSO as size and distance judgement suffered.
The captain banking on to an approach to Angsi Alpha

It was with this thought that we placed our reliance on the beacon, especially seeing that the GPS diamond on the display indicated that Perintis was 15 degrees left, or about 7 miles displaced to the left. This was beginning to be a distraction, so we dismissed the GPS image, and fixed our eyes on the Automatic Direction Finder needle. And there, almost thumbing its nose at us in the murky haze, was FSO Perintis right on track as indicated by the needle. It was relieving, and as Perintis was constantly a copilot's approach, I celebrated coming out of the dark by executing the landing and relaxing in the airconditioned cockpit while the Captain stretched his legs on deck.
The captain on deck Angsi-A with Angsi B in the background

So for any general aviation buff who says offshore flying is monotonous, all I can say is, I haven't died of boredom yet.

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