The 55th 500 Mile International Sweepstakes was held at the Indianapolis Motor Speedway in Speedway, Indiana on Saturday, May 29, 1971. Al Unser, Sr. won for the second consecutive year, dominating most of the race. The race was marred by a crash involving the pace car at the start. Eldon Palmer, a local Indianapolis-area Dodge dealer, lost control of the Dodge Challenger pace car at the south end of the pit area, and it crashed into a photographers' stand, injuring 29 people, two seriously.
Peter Revson started on the pole with a speed of over 178 miles per hour, more than a mile per hour faster than any other qualifier, with defending champ Al Unser in the middle of the second row. Mark Donohue, who qualified in the middle of the front row, took the lead at the start of the race and led the first 50 laps. A mechanical issue ended his day after just 66 laps, and Unser assumed the lead. He and Joe Leonard swapped the lead several times during the middle portion of the race, but Unser led for the final 83 laps, giving him a win for the second year in a row.
Unser (born on May 29, 1939) became the first and only driver to date to win the race on his birthday. It was his second of an eventual four Indy victories. Unser also became the first winner to celebrate in the new victory lane. The new winner's area, now featuring black and white checkered ramps, was moved from the south end of the pits to the "horseshoe" area immediately below the Master Control Tower, near the start/finish line.
The 1971 Indy 500 was part of the newly re-organized USAC Marlboro Championship Trail, in which dirt tracks were separated from the paved ovals and road courses. From then on, the Gold Crown championship schedule would consist solely of paved tracks (both ovals and road courses), giving the national championship a decidedly new look for the 1970s and beyond. In addition, with 500-mile races at Ontario and Pocono now on the schedule, Indy car racing formed its first "triple crown."
The city of Indianapolis celebrated its Sesquicentennial in 1971, and the occasion was reflected on the bronze and silver pit badges for the month of May. During the week leading up to the race, Indianapolis was also the site of 1971 NATO International Conference of Cities.
In the days leading up to the race, Speedway officials announced that female reporters would be allowed in the pit area and garage area for the first time.
For the first time, USAC firmed up the rules regarding pole day qualifying. As had been done in previous years, a blind draw would be held to determine the order of qualifying on pole day. However, starting in 1971, all drivers/cars in the original qualifying draw order would be allowed the opportunity to make at least one attempt in the pole round regardless if rain halted the session and pushed it off to another day. Previously, if rain interrupted the qualifying line on pole day, any cars left in the original qualifying order at the time the track closed (due to rain or at the 6 o'clock gun) were simply out of luck, and had to qualify on the next round.
During practice, McLaren arrived at the track with the new M16 chassis, drawing attention and some controversy due to presence of a large rear wing affixed to the engine cover. USAC rules through 1971 required that any aerodynamic devices were to be an integral part of the bodywork. After inspection, officials ultimately approved the device, as McLaren argued it was part of the engine cover. The engine cover was not much more than a flat, plate-like shape that ran along the top of the engine, with the wing affixed to the rear. As practice began, the McLaren entries quickly established themselves as favorites for the pole position.
McLaren M16 cars dominated qualifying during a record-shattering afternoon. The chassis took 1st, 2nd, and 4th starting positions, with Peter Revson the surprise pole position winner. Revson's four-lap track record of 178.696 mph put the pole position far out of reach for the rest of the field. Penske Racing driver Mark Donohue (177.087 mph) qualified for the middle of the front row, while Bobby Unser in an Eagle chassis, squeezed between the McLaren cars by qualifying third.
Three drivers completed runs, with Bud Tingelstad (170.156 mph) the fastest of the afternoon. Mike Mosley returned after two crashes the previous day, and qualified solidly over 169 mph.
A busy day saw the field filled to 33 cars car. The day concluded with Steve Krisiloff bumping out rookie Sam Posey. 
Strong winds kept speeds down, and only three drivers successfully bumped their way into the field. The windy conditions led to six crashes, and hopefuls waited until the final 45 minutes before they took to the track. The session started out with Mel Kenyon bumping out Carl Williams. Bob Harkey bumped Dick Simon, and Art Pollard got back into the field by bumping Jim McElreath.
Jim Hurtubise once again tried to qualify his front-engined roadster, but on his second lap, hit the outside wall at the head of the mainstretch. His first two laps would not have been fast enough to bump his way in. The day ended as Dick Simon (waved off) and Jerry Grant (waved off) made unsuccessful attempts.
After qualifying, car owner Dick Simon announced he was going to take over the machine qualified by John Mahler. By rule, the car must move to the rear of the grid (33rd) on race day.
For 1971, none of the Big Three auto manufacturers chose to supply pace car for the Indianapolis 500, as the muscle car market had dried up and marketing efforts were shifted elsewhere. Four local Indianapolis-area Dodge dealers, spearheaded by Eldon Palmer, stepped up to supply the fleet of pace cars. The vehicle chosen was the Dodge Challenger 383-4V. Palmer was chosen to drive the pace car at the start of the race.
In preparation for the race, Palmer supposedly set up an orange flag (sometimes reported as an orange traffic cone) in the pit lane to provide himself with a braking reference point. However, there has been some dispute regarding the existence of the marker at all. During the parade and pace lap, Tony Hulman, ABC broadcaster Chris Schenkel, and John Glenn served as passengers in the car. Palmer practiced the run the day before the race.
As the field came down the mainstretch for the start, Palmer pulled into the pits and accelerated down the pit lane. Palmer continued to accelerate, under the impression he was required to cross the start/finish line in the pit area prior to the race cars doing so out on the track. His reference flag (or cone) had been removed and he missed his planned braking spot. Moving upwards of perhaps 125 mph, Palmer realized he was going too fast, and rather than perilously veering back on to the racing surface, he stood on the brakes (the car was equipped with drum brakes) and lost control. The car swerved and skidded to the end of the pit lane, and crashed into a photographers' stand. The stand collapsed, injuring 29 people, however, no people were killed. Dr. Vicente Alvarez, a freelance photographer from Argentina, was one of two on the stand who were seriously injured. Alvarez survived, and died in the late 1990s. Tony Hulman suffered a sprained ankle, and a shaken Schenkel sat out the remainder of the ABC broadcast.
Palmer maintained possession of the car, and eventually it was repaired and restored. In 2006, it was sold to a collector. Reactions of the accident were very critical afterwards, and for the next several years, the pace car drivers selected were either former Indy drivers or persons with racing experience.
Despite the pace car crash near the exit of the pits, the green light came on, and the race continued underway. Mark Donohue grabbed the lead from the middle of the front row.
On lap 12, Steve Krisiloff blew an engine, spilling oil in turn three. Mel Kenyon slid in the oil making contact with the turn three wall. Gordon Johncock and Mario Andretti continued to race each other through three yellow lights. When they arrived at turn three, track workers were on the scene beside the Kenyon machine. Having not heeded the yellow lights, both Johncock and Andretti slid in the oil with Johncock crashing into the Kenyon car, running over the top of it and destroying both cars. Kenyon, fortunately, had seen Johncock coming and dropped back down into the cockpit of his race car. Johncocks car left a tire mark on the top of Kenyon's helmet. The only injury received by Kenyon was a small cut on his shin from the dash board being pushed down onto his legs. All four cars were out of the race, and the yellow light was on for 19 minutes to clean up the accident.
Donohue led the first 50 laps, then the lead traded hands during pit stops between Joe Leonard, Bobby Unser, as well as Al Unser. After leading a total of 52 laps, Mark Donohue dropped out on lap 66 with broken gears. He came to a stop in turn four, and parked the car in the infield, just north of the entrance to the pits.
Lloyd Ruby led at the halfway point.
On lap 111, David Hobbs blew an engine on the mainstretch. Rick Muther spun in the oil, his car veered to the inside wall, then bounced across the track, hitting Hobbs, and lifting up on two wheels. Hobbs' car was pushed head-on into the wall, but he was not seriously injured. Both car slid down the mainstretch, and came to a rest just beyond the start/finish line. The track was blocked except for a narrow portion on the inside where other cars were able to skirt by. The incident happened right in front of Al Unser, who was the leading the race at the moment. The yellow light came on for 12 minutes to clean up the crash.
After a series of pit stops by the leaders under the yellow, the green eventually came back out with Al Unser leading.
With less than 40 laps to go, Al Unser continued to lead, with Peter Revson second, Bobby Unser third, and A. J. Foyt fourth.
On lap 167, Mike Mosley lost a wheel in turn 4. He smacked the outside wall in turn four hard, then bounced across the track and hit the inside wall. Leader Al Unser was ahead of the crash, and second place Peter Revson just slipped by. Third place Bobby Unser spun to avoid Mosley, and hit the outside wall. Mosley's car then crashed into the parked cars of Mark Donohue and Steve Krisiloff, that were sitting near the entrance to the pits. A fire broke out, at which time Gary Bettenhausen stopped his car, and ran to the scene to help. Fire crews quickly doused the flames, and Mosley suffered a broken leg. Bill Vukovich II also spun to the avoid the crash, but he was able to continue. The yellow remained on for 22 minutes to clean up the crash.
The green light came back on with less than 20 laps to go. Al Unser held a comfortable lead, and won his second 500 in a row. Despite four yellows for 53 minutes (about 48 laps), the average speed of 157.735 mph was a new record at the time.First alternate: Jim McElreath (#14, #46)
The race was carried live on the IMS Radio Network. It was carried on over 1,200 affiliates, including shortwave transmission to Europe, Asia, and Vietnam. The broadcast reached an estimated 100 million listeners worldwide. Sid Collins served as chief announcer and Len Sutton served as "driver expert." At the conclusion of the race, Lou Palmer reported from victory lane.
The entire on-air crew remained mostly consistent from 1966-1970. Bob Forbes was assigned as "wireless" microphone, covering the garages and roving reports. The pre-race coverage was 30 minutes long. In a departure from previous years, Sid Collins decided to eliminate booth interviews with celebrities during the race. The only exception was an interview with Hugh Downs, but that was during the post-race coverage. In addition, Luke Walton interviewed Evel Knievel in the pit area during the early stages of the race. Knievel was making his first visit to the 500, as a guest of the A. J. Foyt team.
For the first time, the race was carried in the United States the same day the race was held, on ABC Sports on a same-day tape delay basis. The race was held in the afternoon, and the broadcast aired in prime time later in the day.
The broadcast totaled two hours, and came on-air at 8:30 p.m. (eastern). Among the notable appearances, was David Letterman, at the time employed by then-ABC Indianapolis affiliate WLWI,who served as a roving turn reporter. Letterman interviewed Mario Andretti after he dropped out of the race.
Chris Schenkel began what would be a decade-long tenure as host, while Jim McKay anchor the broadcast as play-by-play announcer. But Schenkel's day as host was short. Riding in (and broadcasting from) the pace car at the start of the race, he was slightly injured when the pace car crashed after coming into the pits at the start of the race.
The broadcast has re-aired numerous times on ESPN Classic since February 2002.