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STS Approach and Landing Test (ALT) Pilot-Induced Oscillation (PIO)

STS Approach and Landing Test, Pilot-induced oscillation (PIO)

Movie Number   EM-0043-02
Movie Date   October 26, 1977
Formats   160x120 QuickTime Movie (.8 MB)
320x240 QuickTime Movie (1.5 MB)
480x360 QuickTime Movie (2.3 MB)
640x480 QuickTime Movie (3.7 MB)
Shuttle landing Still photos of this aircraft are available in several resolutions at

This 21 second movie clip show the STS Approach and Landing (ALT) Pilot-Induced Oscillation (PIO)

During 1977 the NASA Dryden Flight Research Center, Edwards, California, hosted the Approach and Landing Tests for the space shuttle prototype Enterprise. Since the shuttles would land initially on Rogers Dry Lakebed adjacent to Dryden on Edwards Air Force Base, NASA had already modified a Boeing 747 to carry them back to their launch site at Kennedy Space Center, Florida. Computer calculations and simulations had predicted the mated shuttle and 747 could fly together safely, but NASA wanted to verify that prediction in a controlled flight-test environment before the shuttles went into operation. The agency also wanted to glide test the orbiter to ensure it could land safely before sending it into space with human beings aboard.

NASA's Johnson Space Center, Houston, Texas, developed a three-phase test program. First, an unpiloted-captive phase tested the shuttle/747 combination without a crew on the Enterprise in case of a problem that required jettisoning the prototype. There were three taxi tests and five flight tests without a crew in the shuttle. That phase ended on March 2, 1977. The second or captive-active phase-completed on July 26, 1977, flew the orbiter mated to the 747 with a two-person crew inside. Finally there were five flights-completed on October 26, 1977, in which the orbiter separated from the Shuttle Carrier Aircraft (SCA, as the 747 was designated) and landed.

Beginning on August 12, 1977, the first four landings took place uneventfully on lakebed runways, but the fifth occurred on the concrete, 15,000-foot runway at Edwards. For the first three flights, a tail cone was placed around the dummy main engines to reduce buffeting. The tail-cone fairing was removed for the last two flights.

This movie clip begins with the Enterprise just prior to touchdown on the main runway at Edwards AFB after it's fifth and final unpowered free flight.

Shuttle pilots Gordon Fullerton and Fred Haise were attempting a couple of firsts on this flight--a precision "spot" landing on the concrete runway and flying the orbiter without it's tail-cone fairing, since the previous lakebed landing without the fairing had been made by Joe Engle and Richard Truly. Both Haise and Fullerton had prepared as well as possible for the variables of this mission by flying simulated approach profiles in NASA's shuttle training aircraft. However, as with most simulations, the performance wasn't completely identical to that of the real vehicle. Consequently Haise, the mission commander in the left seat, was too fast on the orbiter's landing approach. Deploying the speed brakes, he tried vainly to hit the assigned landing mark but in the stress of the moment, began to overcorrect the vehicle.

The orbiter entered a pilot-induced oscillation or PIO along both it's roll and pitch axis causing the vehicle to begin to "porpoise" down the runway. As it settled down to land it began to bounce from one main landing gear to the next before being brought under control and finally landed by the crew.

Engineers at Dryden later determined that a roughly 270-millisecond time delay in the space shuttle's fly-by-wire system had been the cause of the problem, which was then explored with NASA Dryden's F-8 Digital Fly-By-Wire aircraft and corrected with a suppression filter integrated into the orbiter's flight control system.

Keywords   Approach and Landing Tests; space shuttle; prototype; Enterprise; NASA; Dryden Flight Research Center; Edwards Air Force Base; Rogers Dry Lake; Shuttle Carrier Aircraft; Boeing 747; Kennedy Space Center; Johnson Space Center; Gordon Fullerton; Fred Haise; Joe Engle; Richard Truly; pilot induced oscillation; fly-by-wire; F-8; suppression filter

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