Airbus or Boeing? Part 3

The feel of the VOR (VHF Omnidirectional Range) selector knobs on the old radio navigation head units felt reassuring to twist. The numbers would clack around the frequency drum. Each notch as satisfying and consistent as the last. Cross checking the chart with the navigation log. First to Strumble, then on to Wallasey. Liverpool over the horizon in the black night. We roll and bounce through the darkened clouds. The green glow of the radar screen lights the centre of the cockpit. Between the seats is an inky opening that leads to the cargo deck.

At 11,000 feet we are submerged in a deep layer of frigid cloud. Our fat wings collecting ice, the propellers are flinging chunks of it into the fuselage with loud and irregular cracks. The wing anti-ice system is on. Hot air is being pumped down the leading edge of the wing all the way to the tip. When the air gets there it is blasted out into the atmosphere. This is an unusual system for a turboprop. Most have de-ice ‘boots’ which inflate when required and push off the encrusted ice layer.

In my hands the large control yoke sits at chest height. The hot air rumbling out of the vents rolls across the elevator horns and out into the black night; when the system is on the control yoke plays back and forth against my grip. I flick the ident selector up. Amid the din of the Rolls-Royce Darts and the Dowty-Rotol thrash I listen to the morse code ident of Strumble VOR: dit, dit, dit for ’S’, dah for ’T’, dit dit dah for ‘U’. A short while later the high-pitched DME code cuts through the static repeating the same rhythm.

Click. Off goes the ident selector. A tweak of the left throttle. The left fuel trimmer. The oversized turbine temperature gauge moves a few degrees lower. The beat of the props slows to a steady hum. The fuel counters roll around as I scan across the array of round dials vibrating to the frequency of the aircraft. 50 feet high. I stare at the clumsy horizon bar quivering on top of its hidden gyroscope. The white symbols are yellowed and cracked with age and vibration. In this light it looks yellower.

The captain is pinching across the bridge of his nose, his glasses pushed up on his fingertips. He blinks to fight away the night and rummages in his pocket for his pouch of pipe tobacco. Nose down one bar-width. Pressure on the yoke. A thumbful of trim wheel. The small, wedge-shaped window is leaking beads of rainwater in through its front edge. It migrates forwards, gently soaking the cloth tucked in the crook between the leather-padded top of the instrument panel and the window frame. The altimeter hand moves stickily back to zero.

Down there stands the VOR station. A steel structure with a wired array, electricity humming through the transformer. Swept away by the torrid Welsh wind. Maybe it can hear our passage as we feel our way towards Liverpool. The thrum of our motors as we pass through the silent fingers of radio waves that point the way? In the oil-can din of the freight deck I can hear a spare freight net knocking against the bulkhead. The gentle yawing of the nose sets out an uneven tempo. If I turn around and strain I can probably make out the mail sacks pinned beneath the grey cargo nets.

Beacon. Time, turn, talk. Clack, clack, clack on the frequency selectors. Spinning the OBS as I make good a heading for Wallasey. The yellow needle on the Radio Magnetic Indicator (RMI) pointing the way. Ident. Tweak, trim. Such was the natural rhythm of the night. No autopilot, no TCAS, no screens, no line to follow, no EFB. The night freight business of the mid-90s tended the embers of the type of navigation that had existed since the second world war. This was round-dial aviation at its most traditional and we were the rear guard. An era in retreat. It was laborious, limited and satisfying in unequal measure.

The aircraft of the 80s set off the most extraordinary change in navigation technology since flying at night. The change cracked the lid on accessing difficult and different airports, made flying cheaper and more accessible. If you have flown across the Atlantic then your ticket price is cheaper because navigation accuracy means that the airspace can be more densely occupied than before. If you have flown to a Greek island on holiday then the approach to the airport may well be far safer because now an instrument approach exists where previously the approach struck an apprehensive and uncertain chord.

The navigation story is one of similarity between manufacturers again. The big change was a shift away from using fixed navigation points on the ground to placing long-range point-to-point capability inside the equipment in the cockpit; Advances in micro-computing made it feasible to place the power for navigating around the globe on board every airliner and replace this electro-mechanical version of flying from church steeple to church steeple.

What is left? what is the point of navigating to a place on the ground? Physical infrastructure becomes less and less important. Sure, it took a generation to migrate away from the comfortable habits of the past. But the bridgehead for point-to-point navigation was fixed in place and with it the tantalising prospect of approach navigation that did not rely on shining a beam of radio energy up the approach path, too.

The 737 had a Flight Management Computer (FMC). It still does. Back in the early days of the -300 it was very much an additional navigation box. It didn’t differ significantly from adding a capable GPS navigator to an older light aircraft. It is a bit more integrated on the later 737 EFIS types. It felt more like the heart of the aircraft. But the -300/400/500s that I flew had traditional navigation radios that were capable of being auto-tuned from the FMC. Lots of separate boxes; the aggregator for this information was the pilot.

The 757/767 began converging navigation capability in to one place: the FMC started to become the centre of operations for the aircraft. The radio boxes were still there but their default position was to be controlled by the FMC. The pilot moved from being the aggregator of information to being the beneficiary of it. Not that this was well understood in the early days of entry to service of these new types; “What’s it doing now?” was the joke. It got very old and very serious very quickly. The shift to super-reliable, self-sequencing navigation marked a concerning abrogation of involvement in the fundamentals of piloting that was the opposite of the design goal. More on that in another instalment but it set about a phenomenon known by some as the “Children of the Magenta

Newer systems drew together IRS, radio navigation information and now satellite position and placed the aircraft amongst increasingly sophisticated database of waypoints, airways, approaches and departures. The navigation system picks appropriate radio beacons on which it can confirm its own accuracy. Deadly accurate became the new normal. The glorious imprecision of the previous age was gone. Mostly. Approximation sits deeply in the pilot brain: embedded since the earliest days of flying training. It is the root of gross-error checking. The last line of defence between a bit of rogue data or typing trouble guiding a big jet precisely to the wrong spot on the planet. Does it look right? It still has a place. Now more than ever.

Art is all around in this highly technical world. The enabling technology for all of the complexity and capability in navigation was the display screen. Old electromechanical instruments are beautiful. Works of art – just take the 8-Ball Flight Director Attitude Indicator (FDAI) from the shuttle programme: truly the Faberge egg of instrumentation. Delicate, intricate, perfect and imperfect. And yet, this display can only represent a tiny fraction of an what an electronic display can render. A picture really is worth a thousand words.

I can look at a map unfolding from the top of my navigation display. I can show the hills in the same place. With elevations. And weather. In the corner I can see how hard the wind is blowing. I can monitor which beacons the system is watching. Messages can let me know the health and accuracy of navigation systems. I can watch traffic, count the airspeed down to a knot or the altitude to the last foot.

Going back to round dials leaves a feeling of nakedness; that something is missing. The digitisation dulls slightly the appreciation of rate of change. Nothing beats a physical needle moving on a dial. But losing that is a small price to pay for a diagrammatical sketch of the outside world. No ‘bar-width’ guesstimates on this attitude instrument. I can select a pitch attitude on a Boeing or an Airbus to better than a quarter of a degree and engine thrust to one tenth of a percentage point.

The Airbus has the edge on integration. The Flight Management and Guidance System (FMGS) plays a direct role in the operation of the autopilot. On the Boeing there is a respectful distance between the two. Like shopkeeper and customer. The navigation system asks for a direction, the autopilot delivers it. The Airbus is a bit more bound up than that. Even the flight control systems slurp up data from the FMGS. I imagine the Airbus quivering with streams of binary flowing down to the wingtips.

Technology fitted to the 757, 767 and 747-400 still splits the vertical and lateral guidance of a final approach into two. There are even separate buttons for VNAV (vertical navigation) and LNAV (lateral navigation). The Airbus chooses to do it differently, combining the vertical and lateral elements into a single mode known as FINAL APP (Final Approach).

Knowing the function of these modes is the key to operating safely. There is meaning in every pixel. Every colour used on the screen is there for a reason. Understanding the flow of these modes, how to access them and how to mitigate the sorts of disruption that daily flying presents is a permanent task. I remember reading an incident report which centred on the difference between a white and a green ‘2’ on the engine thrust display which nearly led to the aircraft running clear off the end of a runway during takeoff.

Rich data, aggregated and intricately displayed has made flying much safer. It has also placed a further demand on pilots to understand and manage these systems to get the best out of them and to avoid the worst. The Airbus and Boeing concepts are very similar in nature. Of course they are; both types share the skinny layer of atmosphere and fly along the same corridors and lines.

The most extraordinary feat has been that the concepts of navigation and flight guidance dreamed up in the 1970s have endured and led the changing airspace design that has unfurled over the following nearly five decades. Perhaps it is a little chicken and egg: that systems design and capability drove the design of approaches and airspace? But for years pilots used buttons and modes that have waited until now to release their full potential.

Next up, hand flying the 767 and the A320.


2 thoughts on “Airbus or Boeing? Part 3

  1. Superb. We still have some Electras in regular mail and cargo use here in NZ; although I’m sure they’ve had plenty added on, I suspect operating them still offers some of the tactile, visceral experience you describe.

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