DES MOINES, Iowa (AP) _ There have been big changes - DC-10s have been modified. There have been small developments - infant seats soon may be mandated for the airlines' littlest passengers.

Much has happened in the year since United Flight 232 came to a fiery, cartwheeling end in Sioux City, killing 112, but one thing is unchanged: Heroes still are unwilling to take credit for valiant acts that saved 184 lives.

Capt. Al C. Haynes, who with his crew and the help of another United pilot on board struggled for nearly 45 minutes to control the balky jumbo jet, is refusing requests for interviews. Haynes, who has returned to flying, gets notes from passengers on almost every flight now.

''He takes it in good stride. He doesn't want to be seen as a hero. It was a team effort,'' said United spokesman Rob Doughty.

Three of four members of the cockpit crew, including Haynes, are back in the air, as are seven of the eight surviving flight attendants.

Firefighters, emergency medical technicians, doctors, nurses and the townspeople of Sioux City, lauded for their response to the crash, its victims and survivors, say enough has been said.

''There are no heroes,'' said Shirley Brown, Sioux City's assistant city manager. ''The people genuinely believe that they just did their jobs that day. They did them well, they were coordinated and they had rehearsed, but they simply did what they had practiced.

''What we're hearing from people is, enough is enough.''

Accolades keep coming. More than 100 communities have requested copies of Sioux City's disaster preparedness plan, Ms. Brown said.

''For us, it was our job,'' said Terry Schmidt, training officer for the Sioux City Fire Department. ''But the community, it wasn't their job. It was just the right thing to do. We're kind of proud of that.''

A reunion of passengers, crew and rescuers is scheduled for Thursday, the anniversary of the crash; a memorial has been commissioned for those who died.

Meanwhile, the National Transportation Safety Board has proposed something of a living memorial - it has recommended infant safety seats be required on airliners.

The Association of Flight Attendants has said one of the victims, 23-month- old Evan Tsau, of Albuquerque, N.M., might have lived if the crash had not wrenched him away from his mother, who survived.

There are countless other reminders of the disaster, from the nightmares of the survivors to the balance sheets of United's insurance carrier, which has paid an average of about $45,000 in damage settlements to more than 40 passengers or to estates of passengers who died.

Dozens of other passengers have sued, saying they want a jury to determine damages, and others are seeking punitive damages against the airline, the airplane manufacturer and engine manufacturer. No trials are scheduled.

The National Transportation Safety Board has not issued its official report on the crash, but NTSB spokesman Ted Lopatkiewicz said the titanium fan disk in the rear engine separated, throwing engine parts like shrapnel through the tail assembly and severing all three independent hydraulic systems.

Since the crash, the Federal Aviation Administration has ordered a new kind of engine inspection in hopes of detecting flaws in the titanium disk.

The inspection has not revealed any more flaws, although six disks made from the same titanium billet have been removed from service.

All of the General Electric-built engines were given on-wing inspections. Before the end of this year, all engines must be removed and disks placed in a water bath for separate ultrasonic inspections.

''Of the 287 (domestic) jets, there are 31 disks that have yet to be inspected in what we call the immersion tests,'' said Bob Guyotte of the FAA's regional office in Burlington, Mass. None has failed to pass, he said.

But the NTSB isn't so sure. On June 18, it urged the FAA to order yet another test in which electrical current is used to detect cracks. United Air Lines already is using the method every time it inspects disks on its fleet.

By July 20, 1991 - two years and a day after the crash - domestic carriers must install devices to prevent a catastrophic loss of hydraulic fluid in the No. 3 hydraulic system, the FAA has ruled.

Should the valve kick in, pilots would lose control of the rudder and the elevators, but pilots still would be able to operate all wing controls and to control the angle at which the plane enters the air stream.

''It was tested in a simulator and then actually installed in an aircraft and flight-tested. It was found to work very well,'' said McDonnell Douglas spokeswoman Elaine Bendel.

Without those controls, Flight 232 couldn't be steered to a runway and was flying at least 60 mph faster than a normal approach. Haynes accelerated his remaining wing engines to guide the crippled plane to Sioux City.

The company has sent 84 repair kits to 14 customers worldwide so far, Ms. Bendel said. A total of 428 DC-10s still are active worldwide. United has 55 DC-10s and has installed the devices - at an estimated cost of $37,800 per plane - in about half of them.

Still, the debate continues on the safety of the DC-10. John Galipault, president of Aviation Safety Institute of Worthington, Ohio, said, ''It's probably got the worst safety record of all the wide-bodies.''

Using figures compiled by the Aviation Information Services Limited of London, Galipault said 17 DC-10s have been lost over the years, twice the rate for Boeing 747s and Lockheed L-1011s. Comparisons on fatalities per million flight hours also are not favorable for the DC-10, he said, with 74 for that airplane, 66 for the Lockheed plane and 61 for Boeing's.

Ms. Bendel blamed hangar fires, terrorist attacks and other causes for the 17 lost airplanes, saying they had nothing to do with the design of the plane. Galipault ''has a personal vendetta against the DC-10, for whatever reason,'' she said.

In the 45 days after the crash, only 400 of some 1.8 million United passengers asked to steer away from DC-10s. But McDonnell Douglas no longer makes the plane; the last one was delivered a week after the crash, and the company is concentrating its efforts on a replacement, the MD-11.

There still are plenty of DC-10s in the air, but there is no United Flight 232.

As is the industry custom after a serious accident, United changed the number on its afternoon flight from Denver to Chicago.