Ask the Pilot

Tough questions after a deadly catastrophe in Brazil. When is a runway "too short"? And, are some of our busiest airports unsafe?

Published July 27, 2007 11:00AM (EDT)

This week, no self-indulgent travelogues or embarrassing confessionals. There's nothing like an air disaster to give this column a good kick in the ass.

"Brazil's worst-ever crash." Seems like only yesterday I was typing those words. It was last September, to be precise, after a Gol airlines 737 collided with a U.S.-registered business jet over the Amazon jungle, killing 155 people. The accident brought heavy scrutiny upon Brazil's civil aviation infrastructure. Air traffic in the country has grown tremendously over the past 10 years, putting intense pressure on its air traffic control network, airports and terminals. The last thing Brazil needed was another, even deadlier crash.

Unfortunately, on July 17, an Airbus A320 operated by TAM Linhas Aereas crashed on landing at São Paulo's Congonhas Airport. The twin-engine jet skidded off the rain-slicked runway, slammed into a row of buildings (including a Shell gas station and one of TAM's cargo offices) and exploded. All 187 passengers and crewmembers perished, as did at least four people on the ground. As of this writing the exact death toll is unconfirmed and may climb. Already the accident is not only Brazil's deadliest ever, but the deadliest ever in all of South America.

Hemmed in by dense neighborhoods, Congonhas is the downtown airport for São Paulo, used primarily for domestic flights. Although physically much smaller than nearby Guarulhos International (GRU), Congonhas is the busiest airport on the continent, handling 18 million passengers annually, and is somewhat notorious for the shortness of its main runway. In the wake of the disaster, much has been made of the strip's relatively meager 6,365-foot length. Almost every news report has referenced this as a probable factor in the tragedy, or even its direct cause. Prior to last Tuesday, numerous crews had complained to authorities about unusually slippery conditions when landing in rainy weather. Only a day earlier, an ATR-42 turboprop belonging to a local regional carrier had slid off the same runway and into the muddy grass alongside. Earlier this year, in a ruling that was overthrown on appeal, residents and politicians had successfully lobbied for the banning of certain-sized jetliners from Congonhas altogether. They may yet get their wish.

Although it is highly likely that the stubby Congonhas runway played a role in the tragedy, a ban may or may not be a useful idea. The relationship between planes and runways is a tad more nuanced than the simplistic accounts you've been reading in the papers and watching on CNN.

"Why would pilots be dumb enough to land on a runway that's too small?" asked an e-mailer who'd been following the story on television. "Are there not specific measurements and rules they have to follow?" This scenario evokes the image of a hapless crew, looking down at an airport from several thousand feet and sizing up the available pavement. "That looks about right," says the captain, and down comes the landing gear. Moments later his judgment is proved wrong as the jet goes barreling through a fence and headlong into a gas station.

That's not how it happens. We hear a lot about pilots needing to possess expert judgment and seat-of-the-pants skill. While maybe that's true, there is almost nothing subjective about choosing where to land on or take off from.

Let's take landings first. Per regulations, no crew is allowed to land on a runway that does not guarantee stopping distance under existing conditions. The plane will not be dispatched to an airport in the first place unless it has room enough to touch down and come to a complete stop within the first 60 percent of the intended runway's total length. The exact stipulations vary country to country, rulebook to rulebook, but that's a fair gauge.

For takeoff, two things need to be assured before any commercial jet begins to roll. First, the plane must be able to climb away safely following an engine failure at the worst possible moment -- that is, at the "takeoff decision speed," or "V-1." Second and no less important, the jet must be able to come to a safe and full stop if the takeoff is aborted at any time prior to that speed. (Think of V-1 as a fulcrum. If there's a problem after V-1, the crew knows the plane will fly and clear obstructions. If there's trouble before V-1, the crew knows it has room to stop. This is called a "balanced field.")

So, either you have the numbers or you don't. But what makes it difficult to dismiss any given runway as "too small" is that the numbers will vary flight to flight, dependent on a host of variables: weight, flap/slat settings, wind velocity, elevation, temperature, barometric pressure and surface conditions. Weight alone can vary by hundreds of thousands of pounds, depending on the fuel, cargo and passenger load. Is the pavement slippery? Winds less than favorable? Autobrakes inoperative or an anti-skid system on the fritz? All of that is factored in. There are charts for these things, and information is sent to the crew via radio or cockpit data link.

Thus there is no consistent minimum length that a plane requires. It depends. Granted, a Boeing 747 at any weight will be too heavy for a lot of airports, but there are plenty of occasions when a large plane at a low gross weight requires less pavement than a smaller plane at a heavy weight. (The Airbus A320, with typical seating for about 150 people, is relatively small.) The accident runway at Congonhas is only slightly shorter than the main runway at Washington-National, on which planes as large as the 757 land and depart daily by the dozen. At New York's LaGuardia, the strips top out slightly longer, at just 7,000 feet; widebodies like the 767, DC-10, and L-1011 have used LGA routinely over the years.

(Consider for a moment the much-hyped Airbus A380, the largest commercial airliner ever conceived, still in trial runs but expected to enter service next year. We're constantly reminded that the plane will be "too big" for many airports. What they are talking about, mostly, is the room required for maneuvering on taxiways and aprons, not runway length. Thanks to its powerful engines and high-lift wing, the A380 will require no more runway than the typical 747, A340, or other widebody.)

It should go without saying, however, that if given the option, a pilot will always prefer a longer runway to a shorter one. While the letter of the law is one thing, the problem with short runways is that they leave less margin for error. And with that, let's go back to São Paulo.

We'll begin by granting the TAM pilots the benefit of the doubt and assume they had assured themselves of adequate stopping distance, at least to the letter of the law. To this point, evidence says the airplane touched down on speed, within the touchdown zone. (And they did not, as was alleged earlier, attempt a rejected landing maneuver -- that is, try to take off again after touching down.) But then we learn that the asphalt of runway 17R/35L was ungrooved. As you've probably noticed looking through airplane windows, most runways are laterally cut by thousands of evenly spaced grooves, which help drain water and improve traction. One of the big gripes at grooveless Congonhas was the presence of puddles during and after rain showers. Standing water is a prime contributor to hydroplaning. No different from when it happens in a car, hydroplaning causes an airplane to skim over the runway upon a thin film of water, unable to properly decelerate or maintain direction. Modern jets like the A320 have highly sophisticated anti-skid systems, but their effectiveness is reduced if the water is deep enough.

Brakes provide the bulk of an airplane's stopping power. But should hydroplaning occur and braking effectiveness is reduced or lost, the emphasis falls to reverse thrust. But guess what? We also learn that one of the A320's reversers may have been inoperative. Sure, planes are certified to fly with faulty reversers, but this would have sacrificed performance that already was marginal.

So now the situation looks like this: We have a landing aircraft at or near its maximum authorized weight, a faulty thrust reverser and a substantially increased danger of hydroplaning.

I hate to do it, but let's backtrack a bit. Maybe we shouldn't give the crew benefit of the doubt. This is only speculation, but did the pilots know standing water was present? Had they crunched all the numbers? Presumably they, and thousands of other pilots, had flown into Congonhas many times before in similar weather, with little or no difficulty. Perhaps, this time, conditions were just a little bit worse. Was the culprit an unforgiving runway, a sense of complacency, or a little of both? We'll find out in time.

In the interim, more than one Brazilian pilot has spoken to the press, calling Congonhas dangerous. I would temper that slightly. It isn't always hazardous, but it can be under particular combinations of circumstances. Over the past week, crews have been refusing to land there during inclement weather, while Brazil's airport authority, Infraero, announced plans for a replacement airport. Both of these gestures seem perhaps overdue. (Now, if the country could only get a handle on its air traffic control problems. Last Saturday, a massive radar outage over the Amazon caused scores of Brazil-bound flights from the United States to turn back or divert.)

Meanwhile, it's hard not to be reminded of the December 2005 incident at Chicago-Midway, in which a young boy was killed after a Southwest Airlines 737 overran a snowy runway and collided with a car. Like Congonhas, Midway is known for its short runways. Unlike Congonhas, however, the strips at Midway -- along with those at LaGuardia, Washington-National and a few other semi-notorious places here at home -- are grooved, well-maintained, longer (albeit slightly), wider and in generally better condition. Some are equipped with crushable overrun barriers.

The truth is, some airports will always be safer than others. Virtually none are categorically unsafe. When pilots speak of certain airports, they often describe them as "challenging." Please bear in mind that "challenging" and "unsafe" are wholly different things. (LaGuardia, for one, handles half a million takeoffs and landings annually; there hasn't been a runway-related accident there since the 1980s.) As in any profession, some tasks are more difficult than others, but well within the capabilities of the people trained to perform them and the machines they're trained to operate.

TAM, incidentally, is South America's largest airline and 20th largest in the world, transporting 25 million passengers each year. The carrier flies 101 aircraft, including about 65 Airbus A320/A319 models laid out in an all-coach configuration. The accident aircraft was outfitted with 174 seats -- 20 or so more than most A320 operators. (This doesn't, by itself, indicate that the ill-fated flight was unusually heavy, as passenger weights are only a fraction of a plane's total heft -- sometimes under 10 percent, even at maximum occupancy.) TAM's founder, Capt. Rolim Amaro, died in a helicopter crash in 2001.

South America's deadliest air disasters:

1. July 2007. A TAM Airbus A320 crashes on landing at São Paulo's Congonhas Airport, killing 191 (unconfirmed).

2. June 1989. A Surinam Airways DC-8 crashes at Paramaribo, Surinam, killing 178. Nine passengers survive.

3. August 2005. In western Venezuela, a chartered West Caribbean Airways MD-82 crashes after a dual-engine failure, killing all 160 on board.

4. December 1995. An American Airlines 757 en route from Miami to Cali crashes into a mountain near Valle de Cauca, Colombia. The crew had misprogrammed the flight's navigation system. All but four of the plane's 163 occupants perish.

5. March 1969. Moments after takeoff, a VIASA DC-9 slams into a neighborhood of Maracaibo, Venezuela, claiming the lives of 155 people, nearly half of them on the ground.

Special thanks to Marcio Pinheiro in Brazil for assistance with this story.

By Salon Staff

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