Flight delays and cancellations have already made 2008 an annus horribilis for airline passengers. And since summer is the airlines' busiest season, tougher times may be coming. (One omen: There were more delays in the summer of 2007 than in the previous three summers.) Here's how to improve the odds of arriving on time.

Leave early. Summer thunderstorms tend to hit in late afternoon. In every July and August for the past four years, more flights left on time between 6 a.m. and 7 a.m. than at any other time, and, as a rule, more departures were delayed between 8 p.m. and 9 p.m. Planes were most likely to arrive on time between 7 a.m. and 8 a.m.

Fly on Saturday. Experts at the National Air Traffic Controllers Association have often noted Saturday as the best day to arrive on time. But each airport has its own peculiarities. For the best days to fly from 29 of the nation's largest airports, go to NATCA's site, at www.natca.org/mediacenter/avoiddelaystips.msp.

Fly in August. During each of the last four summers, more flights arrived on time in August than in July.

Choose an on-time airline. The most punctual U.S. carriers last July and August were based in Hawaii: Hawaiian and Aloha (the latter, ironically, now defunct). See "Who Got There on Time?" (at right) for good and not-so-good choices. Past performance might not be a perfect predictor of flight delays, of course, especially this year: As we went to press, government-mandated maintenance checks were grounding lots of flights.

Take nonstop flights. And avoid "direct" flights that nevertheless stop en route.

Consider different airports. Last August more flights left on time from Dallas Love Field than Dallas-Fort Worth, for example, and more left on time from Chicago's Midway than from O'Hare. To see detailed on-time statistics by flight, airline, or airport, go to the Department of Transportation's site, at www.bts.gov/programs/airline_information.