I never tell business travelers not to fly, because only you know what is essential to your business. But I feel compelled to tell you this: I’ve just informed my own clients that I’m not flying anymore this summer, except in extraordinary and absolutely unavoidable circumstances.

The reasons I’m redlining the summer are obvious: Record flight delays and cancellations. Record amounts of lost or misplaced luggage. Passengers held hostage for hours on runways on cramped, ill-provisioned flights. Business travelers diverted to small airports in tertiary cites and then abandoned as their aircraft flies away empty. Flights across the Atlantic on planes with malfunctioning toilets that spew sewage down the aisles.

I’m no wimp. Three decades of business travel has made me tough and cynical and stoic about the road. But I’m not stupid either. I can do the math: Flying this summer simply isn’t an efficient or cost-effective use of my time or my clients’ money.

But if you must fly this summer, I suggest that you do your best to avoid these guaranteed time-wasting, angst-inducing black holes.

American Airlines Hub at Dallas/Fort Worth
When you combine the on-time, canceled-flight, and mishandled-baggage statistics churned out each month by the Department of Transportation, American Airlines and its commuter carriers are arguably the nation’s least-reliable way to fly. And its huge hub at sprawling Dallas/Fort Worth has the most problems. On some days in June, the airline canceled as many as a third of its D.F.W. departures, according to flight-information site FlightStats.com. Even factoring in the brutal early-summer storms that have hit northern Texas, American Airlines’ cancellations are excessive. Avoid changing planes there.

Northwest Airlines During the Last 10 Days of the Month
Northwest is trying to operate with about 25 percent fewer pilots and co-pilots than it employed in 2000. The inevitable result: massive crew shortages at the end of June when Northwest’s remaining pilots “timed out” and could no longer fly. (According to federal regulations, pilots cannot fly more than 100 hours a month.) Northwest canceled more than 1,200 flights during the last 10 days of June. The final 10 days of July and August won’t be much better.

Continental Hub at Newark Liberty Airport
Continental Airlines is probably running less erratically than any of the six large-network traditional carriers. But its hub at Newark Airport is the most dreadfully overburdened facility in the dreadfully overburdened Northeast Corridor. For the first five months of the year, in fact, government statistics show that Newark experienced more delays than any other airport in the United States. Alternatives? Well, none, since New York’s Kennedy and LaGuardia airports are almost as bad as Newark Liberty.

Delta Hub at Kennedy Airport
Speaking of bad, Delta recently launched a breakneck international expansion at New York’s John F. Kennedy Airport. It now flies to dozens of cities in Europe, Africa, and the Middle East. The problem? Its two terminals at J.F.K. are shoddy and shambolic. About half of its flights run late, according to the government. And its commuter carriers, which bring in connecting international travelers from around the East Coast, run late or not at all. (By the way, J.F.K.’s other big carriers, American Airlines and JetBlue Airways, aren’t models of efficiency either.)

U.S. Airways Everywhere but Phoenix
The merger of the old U.S. Airways and America West Airlines has been an operational nightmare. Its two East Coast hubs (Philadelphia and Charlotte) are deteriorating. The airline was also dead last in systemwide on-time performance in March, April, and May, the most recent months for which there are government statistics. Its recent expansions to Europe and Hawaii are generating complaints due to poor service and frequent cancellations. Worse, the airline is also slashing the number of first-class seats on all its aircraft. If you must fly U.S. Airways, make sure you use its hub in Phoenix, which is running notably better than the rest of the airline’s system.

Southwest Airlines at Baltimore/Washington International
Despite its all-coach configuration and its continued policy of not offering assigned seats, Southwest Airlines has gained favor with business travelers because it is fairly timely and efficient for short-haul flights. But avoid Southwest at Baltimore-Washington Airport. The airline seems understaffed there, and even Southwest’s vaunted point-to-point flying system isn’t immune to East Coast thunderstorms.

United Airlines Flights to Asia
Seventeen months removed from the longest and costliest bankruptcy in airline history, United Airlines is running on fumes. Its fleet is old and tattered, and its in-flight service has been slashed. Many of its flights (its “Ted” service) have no first-class seats at all. But United fares most poorly on its Asian routes, where top-notch competitors such as Singapore Airlines, Cathay Pacific, and All Nippon Airways fly newer planes with dramatically better business- and first-class amenities.

Airports of the Damned
If it were just the airlines that were running poorly, life on the road this summer might be bearable. But some of the world’s most important airports are overwhelmed too.

In Asia, Tokyo’s Narita Airport is overburdened with flights and is unreliable and unpleasant as a connecting facility. Instead, change planes in Seoul if your destination is northern Asia. If you’re headed to Southeast Asia, try Singapore, Kuala Lumpur, or Hong Kong. Bangkok’s Suvarnabhumi Airport is less than a year old, but it is dirty, crowded, and plagued by shoddy construction. Avoid it too.

In Europe, Milan’s Malpensa Airport is generally considered the worst choice on the continent to change planes. Charles DeGaulle Airport in Paris is under construction and has never been a good place to change planes. Hardcore business travelers have always liked compact and efficient Schiphol Airport, outside Amsterdam, but baggage handling there is notoriously poor in the summer. We already covered some of London Heathrow Airport’s problems in last week’s column (Read "Later, London"). If you need to change planes in Europe, try Munich (relatively new and quite pleasant), Vienna (compact, with good connections to eastern Europe), or Copenhagen (efficient, with good connections throughout northern Europe).

Notably bad in South America is Brazil, where the air-traffic-control system is horrendous. Most African airports are hopeless too, although Johannesburg is workable for connections to the southern part of the continent. If you’re headed elsewhere in Africa, try connecting in Dubai or Abu Dhabi, where the Arab carriers are flush with cash and making an effort to connect to Africa’s leading business centers.

The Fine Print
Most business travelers can avoid overscheduled Fort Lauderdale Airport by flying to West Palm Beach or Miami instead. But if you’re trying to catch a cruise and need to use Fort Lauderdale, leave a day early. Ditto for Seattle-Tacoma, where the airport is often overwhelmed during the height of the summer cruising season.