The Vibration

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By: Mark H. Goodrich – Copyright © 2013

Bill first noticed the vibration – or whatever it was – as the gear retracted and he called for the flight engineer to set climb thrust. Gone as quickly as it occurred, he scanned the forward engine instruments for some indication of what it had been, but everything seemed normal. Well, at least as normal as it could be with inter-mixed engine models. He shook his head slightly as he watched Tim adjust the thrust levers, each ultimately split by several inches from the others. When moving them to takeoff thrust just a minute or so earlier, he had stopped the forward movement when one engine reached maximum thrust limits, and immediately noticed the divergence of power between the four engines with equivalent lever positions. Having started as a mechanic himself, Bill knew that rigging the thrust levers properly on the seven-four-seven was not that difficult, yet the company had been unwilling to spend money for maintenance deemed by non-pilot managers to be unimportant. He turned to scan the engine instruments on the engineer’s panel, purposefully watching each gauge for a few seconds, but seeing nothing amiss. “Did you feel anything unusual with the power reduction,” he asked Tim? “No sir, skipper. Everything seemed normal to me.”

TheVibration(2)(RtFwdFuselageB747)Bill leaned forward to adjust the flight deck lights. Darkness in the sky over Africa was always surprising. It was as though any dusky twilight between penumbra and umbra did not exist. One moment the horizon glowed with what remained of light from the setting sun, and the next it was cloaked in darkness. Maybe it was just the absence of ground lights over so much of Africa, but without moonlight, it seemed deeper than merely dark. What was it that his father used to say about dark nights on the farm… “like the inside of a cow”?

Light from the stars was still shielded by clouds above, and the few lights below had been obscured by an undercast as they climbed. Flying north from Johannesburg, the glow of the metropolitan area had dimmed quickly behind them. The route was familiar to Bill. In fact, it was all too familiar, which was the best reason to take nothing for granted. Indeed, it seemed that every flight included at least one event to be noted in his mental encyclopedia, as well as in the personal logbook. Reading the brief entries later always engendered a volume of detailed memories about an entire flight.

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He turned to look at the vibration meters at the bottom of the engineer panel, but they all now read zero, of course. When the seven-fours were new, the importance of monitoring engine vibrations had been emphasized. Then, as more powerful versions of the engines were installed, maintenance write-ups on most flights reflected engine vibrations exceeding the maximum limits. When neither airline maintenance nor the engine manufacturer could solve the vibration issues, the maximum limits were raised, and then raised again. Rather than spend money for new instruments, new “red lines” had been painted on the glass faces. Finally, the instruments were simply disconnected, with the explanation that vibration levels had never really been an important issue anyway. The tension between economics and safety was consistent, if nothing else. So, here he was with a possible vibration issue and the meters that could identify a problematic engine had been rendered unusable. Once again, short-term corporate profits trumped flight safety and long-term maintenance costs.

Bill always briefed co-pilots and engineers on the need to watch for traffic over Africa, but it was the unusual crewmember that appreciated the potential seriousness until personally experiencing a near collision. Stories of such events never made the same impression as watching another airplane flash by, mere feet away in the midst of an evasive maneuver. Just keeping some crewmembers awake was a challenge – getting them to look outside, as well, could be all but impossible. He looked over his shoulder at the engineer station, and saw that Tim was recording fuel use data. The co-pilot was looking forward, but seemed to be focused on infinity. Bill picked up the flight release to check his name. He must have known someone named Jim who looked like this kid because that name popped into his head every time he looked at him, but this one was Larry.

Star glow suddenly exploded into the flight deck as they topped the highest cloud layer, and Bill saw young Larry flinch at the surprise of it. There was no moon, and the galaxy as seen in the southern hemisphere was vibrant. Bill thought of how people who had seen only the northern hemisphere would be amazed at the difference, with vastly more stars and cosmic dust. To understand why it was called the Milky Way, one truly had to see it from the southern half of the planet.

The warning horn sounded their approach to the assigned cruising level at three-five-zero. A clicking noise confirmed that the altitude select knob had switched off. Bill began to push the nose over slightly, slowing the rate of climb, as autopilots always seemed to need a little help to level off accurately. As the altimeters showed an even three-five-zero, he moved the switch to altitude hold, and watched closely as the autopilot began to trim forward. The younger pilots trusted autopilots without question, but Bill always held his hand just above the control wheel when a new autopilot mode was engaged until he was certain it would do as commanded. As the speed came up to Mach .84, he called for cruise thrust. Tim reached forward to begin setting and fine-tuning the thrust levers. Everything seemed normal as Tim matched up the engine speeds. Some engineers liked to align on engine pressure ratios, others on N1 or N2 speeds, and still others on fuel flow. Tim was an N2 guy.

There it was again, and gone just as quickly as before. Bill switched the autopilot off and gently cradled the control wheel, trying to feel if there was any vibration in the flight control system. It all felt normal. He selected the yaw dampers off and then on individually. Again, everything seemed normal. Larry turned to look at Tim. Tim shrugged, laughed and made a comment about the onset of dementia as captains aged. Bill ignored the joke, illuminated the wings and sent Tim back to look for any floating spoiler panels.

Bill’s focus was split between the instruments inside, and keeping a watch for any renegade DC-8s outside. Even airlines that held operating certificates often evaded overflight permit fees by flying without flight plans or clearances from air traffic control, and it seemed the airspace over Africa was saturated with what had come to be called “ghost planes”. Bill shook his head as he looked at the newly installed traffic collision avoidance system. The regulator required that TCAS be installed, but there was no rule to prevent an airline from minimizing costs by installing a hopelessly ineffective model. Management bought the cheapest possible system to meet the requirement, with the presentation crammed into the face of the vertical speed indicator, and then only on the captain’s side. “What a joke”, he thought. With a twelve-mile scale and everyone moving at eight or nine miles a minute, the warning of another airplane closing was 20 seconds or so even if one happened to be looking right at it when conflicting traffic first appeared. Airline executives and regulators certainly had no idea of just how long it takes to change altitude and heading on a seven-four-seven, but in the thin-air of high altitude at more than 800,000 pounds, it was far from nimble. Like everything else in the safety end of the business, it would take an accident before industry accepted that, while this technology sounded good in a press release, as implemented it was just another whitewash deal. Unless wreckage fell into the proverbial school yard, it might take more than one collision, and certainly one between two cargo jets over Africa would not result in enough headline ink to get anyone’s attention.

Masvingo was the next radio station, and it was a crossroad of highways in the sky. Bill thought about the folly of how the “all stations” traffic calls in the blind were mandated, using a procedure that dated back to when air traffic over Africa was mostly DC-3s flying at 140 knots. It remained unchanged, even though jet speeds were now 450 knots and higher. Procedure dictated a call five minutes before crossing a station, announcing departure and destination airports as though that was of any value in collision avoidance, but still did not require one to identify airplane type. Expecting at least a quizzical response, if not an argument, he told Larry to make blind calls at ten minutes, five minutes and two minutes before station passage, and to include the airplane type with the required information. Larry seemed to sense Bill’s tension level, and offered no argument. The kid was learning.

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The vibration had not been much, but Bill kept thinking about it. He recalled one older captain with whom he had flown in his early days with the airline. The man preached contingency planning, and said professional pilots were paid to avoid making the same mistake once. Bill began to think about a potential diversion, just in case they lost an engine. Johannesburg to Nairobi is a lonely route once past Lilongwe, and it was the next station. Zanzibar was all but the same distance as Nairobi, and the airline had no maintenance support there anyway. This was the kind of situation where one was thankful to be in a seven-four-seven, with its four engines, and redundant systems design. So long as an engine failure was not accompanied by fire or shrapnel damage, continuing with an engine out was not really unsafe, like it was with two-engine airplanes. Safety – that was another thing the oversight agencies rationalized as they bent under corporate pressure, and loosened the rules for using two-engine airplanes in order to save a little fuel expense.

The glow of Lilongwe on the undercast was fading behind them – 800 miles to go. Bill turned to Tim. “We should write something up about that vibration.”

“What vibration,” asked Tim? “I wouldn’t even know what to write, and you know how the vee-pee technical reacts if we put something in the log with no broken part. Hell, he tries to talk us out of spending money for maintenance even when we do have a broken part.”

Tim was right, of course. Bill returned his attention to scan for traffic. Lake Tanganyika was off to the west, but with no ground lights, no moon and an undercast, it would pass unseen even if they were above it directly. He sighted a rotating beacon below and crossing, then checked the TCAS, and chuckled again. The traffic was probably 25 miles out, at least twice the maximum display distance for the TCAS. In this case it would be no problem. The airplane would pass well in front of and below them. It was at least another three-hundred miles before the Nairobi radio signal would be strong enough to use. They were already over higher terrain, and if the weather held as forecasted, Kilimanjaro would be unseen this night from above or below the clouds. Bill had been to Nairobi a hundred times, but the habits of a career kicked in, and he picked up the chart to verify his recollection of the minimum safe altitudes in the southern quadrants was correct.

He knew that Tim and Larry would prepare the landing data cards in another two-hundred miles or so, but what if they were busy then with an engine failure? Bill pulled up the power and speed charts, filled in a data card himself, and handed it to Tim for an accuracy check. Tim smiled and shook his head slightly. They had been flying together for at least ten years, and Bill knew that Tim knew he was reducing the work load for arrival, just in case.

As Africa rolled by unseen beneath them, the distance measuring equipment came to life on the Nairobi station frequency, Larry was picking up the current field conditions, and Tim leaned the landing data card up against the center instrument panel, where both pilots would be able to see it easily. Bill called, set and cross-checked the bug speeds, gave the descent and approach briefing, ran his flows and called for the checklist.

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Pulling the thrust levers back to initiate the descent, Bill called for the engine anti-ice and waited, but the unusual vibration was absent. Into the clouds a few minutes later, he tightened the shoulder straps, and moved the rudder pedals closer. Light turbulence began to gently rock the airplane. As the runway came into view at six-hundred feet, he toggled the autopilot off, watched for the vertical descent to flatten at 280 feet as ground effect started to become a factor, and reduced thrust slightly to compensate. At 30 feet, Bill reduced thrust to idle, began adding some back pressure to flare, and recalled how pilots wondered when the seven-fours were new about whether they could land from a seat forty feet above the wheels. They need not have worried, as it turned out to be easy and natural. As the main gear tires began to spin up at touchdown, he felt the autobrakes cycle and the ground spoilers deploy, and gently lowered the nose gear tires to the runway.

Tim called the arrival at 2334 local. With the shutdown checklist completed, Bill saw the cargo and fuel trucks pulling into position, and the next crew walking towards the airplane for the Nairobi to Amsterdam leg. The line chief appeared and Bill mentioned the vibration, suggesting that a special look for oil leaks or other engine issues might be wise before the airplane departed. The next crew was waiting at the bottom of the portable stairs, and Bill also mentioned the vibration to Charles, the next captain and one of the better young captains, who had upgraded just one year before after a decade in the co-pilot’s seat.

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A few minutes later in the flight operations office, hot coffee in hand, Bill and Tim were completing the flight documentation for the station manager, when the company frequency on the office radio crackled to life with a report from the airplane they had just parked.

“Ops, flight four-thirty-four. Engine Number One just blew up during start. The fire trucks are on the way, but it looks like we got it shut down with no fire. Line maintenance is already here. You’d better let London know right away. And, tell Bill thanks for the heads-up regarding the vibration he noticed. Because of his warning, we were watching the engines very closely during the start procedures, and caught the over-temperature on Number One when it first went hot. Catching it early probably saved the company a lot of money.”

Bill suddenly realized that everyone in the room was staring at him.

“How did you know,” asked Larry?

Bill just shrugged his shoulders at Larry in mute response. He didn’t know precisely how he had known that something was wrong, but that was the nature of how experienced pilots came to understand their airplanes over time in the captain’s seat. With some five-thousand hours on various models of the seven-four-seven, he had been conditioned by the cacophony of noises, vibrations and pressure changes. In fact, he often initiated control input pressures in response to such inferences even before the flight instruments reflected any need for a correcting input. Clearly there had been no significant vibration during the flight. If there had been, Tim would certainly have picked it up. It just hadn’t felt right somehow, and he still could not put his finger on what it was that repeatedly caught his attention throughout the flight.

The crew van pulled up, and they climbed aboard for the short ride to the hotel. Ten hours of rest, then on to Luxembourg, and London next. Bill wondered if the grass would need cutting when he got home.

 Mark H. Goodrich – Copyright © 2013

“The Vibration” was first published in the February 2014 Issue (Vol 11 No 1) of Position Report magazine.