Ask the pilot

The Great Circle Mapper hypnotizes the pilot. Also, how far can a plane go after losing an engine?

By Patrick Smith
Published March 4, 2005 8:30PM (EST)

My three-week-old moratorium on discussions of maps and great circles is hereby suspended. The reprieve is needed in order to hype my new favorite Web site, Karl Swartz's Great Circle Mapper. My ability to spend long hours at this page feeding in random city pairs, mesmerized by the connectorial magic of countless red lines, offers discomfiting insight into the minds of those infatuated both with flight and geography. Nonetheless, I've yet to find a source that more adroitly illustrates the shortcomings and fallacies of the average wall map or atlas. Never again will I sigh and stammer when presented with the question, "Why does my flight from Chicago to Hong Kong fly over goddamn Siberia?"

My old answer was a groping dissertation on cartographic projections and how to visualize spheres. My new answer is: because. Mapper can do the rest. It takes only a second: Go to the Paths box and type in "ORD-HKG." Hit the Display button, and behold. A few thousand pixels exponentially more useful than any of the Pilot's mangled syntax.

In fact, freeze right there, gazing down upon the Arctic (note also the more correctly rendered Greenland, as compared to the monsterized version presented by Mercator et al.). Without touching another key, locate California and France. Notice the shortest path between San Francisco and Paris takes you above the southern tip of Greenland. Return to the Paths box and enter "SFO-CDG" to see the actual tracing. This may help avoid incidents like the one a year ago when a group of Paris-bound passengers, watching their route unfold on the bulkhead progress screen, were induced to near panic in belief their flight had been hijacked. It took an announcement from the captain to explain why the aircraft seemed headed for the North Pole instead of Charles de Gaulle.

As a bonus, Mapper gives latitude and longitude coordinates for each airport, as well as mileage totals of all pairings (though somewhat worrying is that teasing disclaimer: "This information may not be accurate...").

I asked Karl Swartz how Mapper does its magic. "I use software from the PROJ.4 package to do the math," he tells us. "But it's just spherical geometry to compute the geodesic, fiddled a bit to adjust for the fact that Earth is not exactly a sphere."

People who speak of "just" spherical geometry make me nervous, so I kept my mouth shut and let Swartz keep talking.

He points out other goodies available on the site. One of the most intriguing, particularly for those of you looking to dodge an arrest warrant or crumbling marriage, is the Locations feature that automatically determines the most distant earthly airport from a chosen point. If I feed my hometown BOS into the Locations box (followed by a double click on the resulting data), I'm informed that Margaret River, Western Australia, is the farthest airport I can possibly fly to.

"I'm not sure it has much practical value," says Swartz. "But I suppose you could use it to settle debates about whether or not you'd end up in China if you dug straight down. Yes, if you live in Argentina."

Once you're feeling comfortable, or addiction is setting in, have a look at "SVO-SCL." Presently there's no direct service from Moscow to Santiago, Chile, but notice the way this imaginary flight traces two great circles, mirrored arcs on either side of the equator evinced through a delicate figure-S. Yes, the bottom of the world is no less round than the top. Try typing "GIG-SYD" (Rio de Janeiro-Sydney) to view one of the more dramatic southerly crossings. Note the passage over Antarctica enjoyed by those aboard Qantas or Varig on a trip from South America to Australia.

Except maybe not. The shortest distance isn't always the most practical one, and the beauty of a great circle is often sent zigzagging by geopolitical frictions, exorbitant airspace fees, and the rulebook of something called ETOPS -- restrictions placed on aircraft with fewer than three engines.

ETOPS (extended twin-engine operations) was pioneered by TWA in the mid-1980s, when that carrier, after extensive planning and under careful sentry of the FAA, commenced Boeing 767 service across the North Atlantic, a field previously dominated by three- and four-engine machines like the 747 and DC-10. Twin-engine long hauls soon became commonplace across vast stretches of ocean, subject to remaining within certain distances of diversion points at all times. Midway Island, for example, in the Pacific. Or Keflavik, Iceland.

Last month in Everett, Wash., Boeing rolled out the 777-200LR. The suffix is for "long range," and this newest variant of the widebody twin is the longest-legged commercial aircraft ever built. (Pakistan International and Taiwan's Eva Air are in line to be the first customers.) Obviously the stigma of operating great distances on only two engines is a thing of the past. Indeed, U.S. and foreign aviation authorities are reorganizing the long-haul rulebook under the simpler, less numerically specific umbrella of "EROPS," or extended range operations.

No plane ever crashed from ETOPS-related engine trouble, and in essence the restrictions have less to do with crashing than with diverting. High over the middle of nowhere, should a four-engine 747 or A340 suffer the demise of a power plant, it can, in the majority of cases, carry on toward its destination or suitable alternate field along the way. Even with a second failure, rare as such occurrences are, the plane would remain adequately flyable. Should a twin-engine jet lose an engine, however, the situation is obviously more precarious, and a prompt diversion is expected. Thus, it isn't about ocean; it's about distance to approved alternate runways. From an ETOPS/EROPS point of view, the vastness of empty desert or frozen tundra is no different from that of the open sea.

A single unplanned pit stop can cost an airline hundreds of thousands of dollars. For manufacturers, much rides on the reliability of their airframes and engines.

I've noticed a quirk in Continental's taxiing procedure: It seems that immediately after landing they shut down one of the plane's engines. Is this my imagination, or is it another cost-cutting strategy? Is that much fuel really burned while taxiing?

Airlines have been doing this for decades, though nowadays they're quicker than ever with the cut-off levers. With oil prices hanging near $50 a barrel -- the cost of jet fuel rose 56 percent between 2003 and 2004, peaking at almost $1.60 a gallon last October -- airlines have become hard-edged conservationists of sorts. Planes will routinely taxi in, and out, with a power plant shut down, the remaining engine(s) and auxiliary power unit (APU) supplying air conditioning, hydraulics and electrics. On a two-engine aircraft, the lowest power setting, aka "idle thrust," from one motor is usually enough, or almost enough, to keep it taxiing. Idle thrust from both engines often wastes energy by requiring crews to ride the brakes.

To pick one, the MD-80 (a twin-engine narrowbody with seating for about 140) will save 2.4 gallons per minute on a single-engine taxi. If a trip to or from the runway takes seven minutes (hopeful in many cases), that's close to 34 gallons per flight (17 per taxi in/taxi out). Using the January 2005 average price per gallon of $1.30 presents a savings of about 44 dollars. Assuming an MD-80 flies three legs in a day, that's $132 per day, per aircraft. For a carrier like American Airlines, with more than 350 MD-80s in its fleet, the saving would be at least $46,000 per day, and more than $16 million a year, on that model alone.

Theoretically anyway. American claims it saved $2 million last year through increased use of single-engine taxiing. As you might expect, such procedures aren't always practical or possible. The rules vary markedly between airline and aircraft type, and they are subject to a slew of fine print -- weather conditions, mandatory cool-down or spool-up times, etc.

The price of jet fuel, much like that of automobile gasoline, varies from region to region, airport to airport. A gallon in Houston might run 5 cents less than in New York, a gallon in Singapore a nickel cheaper still, subject to any number of local taxes, fees and add-ons. This is one of the reasons planes sometimes "tanker" extra fuel between cities.

After considering the ETOPS and single-engine taxi, undoubtedly a number of people will be wondering about something, so allow me to make the following declaration: Under no circumstances do crews shut down engines during flight to save money.

But, to think outside the box for a moment, why not? If a four-engine plane can fly just on three engines, or even two, why not put one to sleep for a few hours over the ocean?

During flight, the repercussions of a shut-down engine are vastly different than on the ground, affecting everything from cruising speed to altitude to pressurization. While perfectly able to compensate for one another in the event of inflight failure, engines are not designed solely in the interest of redundancy. They work together.

For example, losing an engine over the ocean, seldom as it happens, typically mandates a reduction in speed and a descent to a lower altitude. High altitudes mean thinner air, and you need more power to cruise there (certain aerodynamic issues also come into play). And once the speed/altitude variables shift, so do those of range -- to the intended destination and to any required diversion points.

In other words, an expired engine requires recalculation of the entire flight plan. Even with four engines this can mean a midflight detour (hello, Keflavik, or Anchorage). Not because the plane is on the verge of crashing, but because all of the range and performance parameters have shifted. The demanded descent and other aerodynamic penalties increase fuel consumption and may in turn require even more fuel than is "saved" by the dead motor.

This was illustrated wonderfully in late February, when a British Airways 747 headed for London lost one of its four Rolls-Royces shortly after takeoff from Los Angeles. In a move that garnered press attention and sparked something of a furor, the crew pressed on for England rather than return to LAX. An unorthodox decision, and, to go on the record, not one I'd endorse myself, but perhaps not altogether stupid or dangerous, considering the 747's capabilities on three, or even two, engines, and the extreme improbability of a second failure. After running the numbers, it was determined the flight would have sufficient fuel to continue safely. "That's not something our own company would have allowed," says Michael [last name withheld], a 747 first officer with a major US airline. "But in a way I can sympathize, and it's not as crazy as it probably sounds to the layperson."

Pilots do not make such critical decisions entirely on their own. Crews work in concert with an airline's dispatch department (known assortedly as flight following, flight control, and such), with whom they remain in contact for the duration of the journey, weighing the advice of various technical staff. That being said, the ultimate and final authority rests with the captain. "You can be assured," adds Michael, "no crew would have accepted the recommendation to keep flying had they thought the idea was unsafe."

Was British Airways, with the captain's blessing, acting on behalf of financial concerns? Partly, sure, but that in itself isn't tantamount to recklessness.

Unfortunately, BA268 encountered lighter-than-expected tailwinds (those are different from the purported "stronger headwinds" you'll read elsewhere), and when the amount of remaining fuel began to fall below target values at en route waypoints, the captain realized a diversion to Manchester would be prudent. The fuel-progress portion of a flight plan, amended or otherwise, can go on for several pages. Burn totals (actual versus anticipated) are carefully cross-checked numerous times en route. The plane was not "running out of fuel," as the Times so crudely put it. Less dramatic, but more accurately, the 747 would no longer have met the reserve buffer should delays or a holding queue have struck near Heathrow.

But that's no fun for the Times, which prefers conjuring up images of a goggled aviator tapping on a gauge and exclaiming, "Yikes! We'd better put her down, mate."

On Tuesday the affair made an appearance in Scott McCartney's "The Middle Seat" column at the Wall Street Journal. I enjoy Scott's work, but the affection may or may not be mutual now that I'm formally upbraiding him for repeated use of the annoying "British Air" bastardization. McCartney also states: "For U.S. airlines, Federal Aviation Administration regulations require commercial carriers to land at the nearest suitable airport after an engine failure."

This is only true for aircraft with fewer than three engines. Exemption 121.565(b) of the Federal Aviation Regulations allows the pilot in command of a three- or four-engine commercial transport to continue onward, subject to a reasonable series of weather and fuel stipulations (though an airline's in-house rules may trump the regs).

McCartney goes on to write that flight 268 flew "up near the North Pole" as it hobbled to Heathrow. He has the right idea, but he's a good thousand miles off course (magnetic or true, for those of you who know the difference). Hasn't he seen the Great Circle Mapper?...

- - - - - - - - - - - -

Do you have questions for Salon's aviation expert? Send them to AskThePilot and look for answers in a future column.

Patrick Smith

Patrick Smith is an airline pilot.

MORE FROM Patrick SmithLIKE Patrick Smith

Related Topics ------------------------------------------

Air Travel Ask The Pilot Business