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The controlled impact demonstration

The Controlled Impact Demonstration (or colloquially the Crash In the Desert) was a joint project between NASA and the Federal Aviation Administration (FAA) to test the impact of a Boeing 720 aircraft.

Contents

History

Practice approach
Slapdown

The National Aeronautics and Space Administration (NASA) and the Federal Aviation Administration (FAA) conducted a joint program for the acquisition, demonstration, and validation of technology for the improvement of transport aircraft occupant crash survivability using a large, four-engine, remotely piloted transport airplane in a controlled impact demonstration (CID). The CID program was conducted at the Dryden Flight Research Facility of NASA Ames Research Center (Ames-Dryden), at Edwards, California, and was completed in late 1984. The objectives of the CID program were to demonstrate a reduction of postcrash fire through the use of antimisting fuel, acquire transport crash structural data, and to demonstrate the effectiveness of existing improved seat-restraint and cabin structural systems.[1]:1

The additive FM-9, a high molecular-weight long chain polymer, when blended with Jet-A fuel, forms antimisting kerosene (AMK). AMK had demonstrated the capability to inhibit ignition and flame propagation of the released fuel in simulated impact tests.

In addition to the AMK research, NASA Langley Research Center was involved in a structural loads measurement experiment which included having instrumented dummies filling the seats in the passenger compartment. Before the final flight on December 1, 1984, more than four years of effort passed trying to set-up final impact conditions considered survivable by the FAA.

AMK cannot be introduced directly into a gas turbine engine due to several possible problems such as clogging of filters. The AMK must be restored to almost Jet-A before being introduced into the engine for burning. This restoration is called "degradation" and was accomplished on the 720 using a device called a "degrader". Each of the four Pratt & Whitney JT3C-7 engines had a "degrader" built and installed by General Electric (GE) to break down and return the AMK to near Jet-A quality.

Over a series of 14 flights, General Electric installed and tested four degraders (one on each engine); and the FAA refined AMK (blending, testing, and fueling a full size aircraft). During the flights the aircraft made approximately 69 approaches, to about 150 feet (46 m) above the prepared crash site, under remote control. These flights were used to introduce AMK one step at a time into some of the fuel tanks and engines while monitoring the performance of the engines. During those same flights, NASA Dryden also developed the remote piloting techniques necessary for the 720 to fly as a drone aircraft. An initial attempt at the full scale test was scrubbed in late 1983 due to problems with the uplink connection to the 720. If this failed, the ground based pilot would no longer have control of the aircraft.

Test

Pre-impact

On the morning of December 1, 1984, a remotely controlled Boeing 720 transport took off from Edwards Air Force Base, California, made a left-hand departure and climbed to an altitude of 2,300 feet (700 m). The aircraft was remotely flown by NASA research pilot Fitzhugh Fulton from the NASA Dryden Remotely Controlled Vehicle Facility. All fuel tanks were filled with a total of 76,000 pounds (34,000 kg) of AMK and all engines ran from start-up to impact (the flight time was 9 minutes) on the modified Jet-A. It then began a descent-to-landing to a specially prepared runway on the east side of Rogers Dry Lake. Final approach was along the roughly 3.8-degree glideslope. The landing gear remained retracted.

Post-impact 1

Passing the decision height of 150 feet (46 m) above ground level (AGL), the aircraft was slightly to the right of the desired path. The aircraft entered into a situation known as a "Dutch Roll". Slightly above that decision point at which the pilot was to execute a "go-around", there appeared to be enough altitude to maneuver back to the centerline of the runway. The aircraft was below the glideslope and below the desired airspeed. Data acquisition systems had been activated, and the aircraft was committed to impact. It contacted the ground, left wing low, at full throttle, with the aircraft nose pointing to the left of the centerline.

Post-impact 2

It was planned that the aircraft would land wings-level and exactly on the centerline during the CID, thus allowing the fuselage to remain intact as the wings were sliced open by eight posts cemented into the runway (called "Rhinos" due to the shape of the "horns" welded onto the posts). The throttles were to be set to idle. The Boeing 720 landed askew. One of the Rhinos sliced through the number 3 engine, behind the burner can, leaving the engine on the wing pylon (which does not typically happen in an impact of this type). The same rhino then sliced through the fuselage, causing a cabin fire when burning fuel was able to enter the fuselage. The cutting of the number 3 engine and the full throttle situation was significant as this was outside the test envelope. The number 3 engine continued to operate, degrading the fuel and igniting it after impact, providing a significant heat source. The fire and smoke took over an hour to extinguish. The CID impact was spectacular with a large fireball created by the number 3 engine on the right side, enveloping and burning the 720 aircraft. From the standpoint of AMK the test was a major set-back. For NASA Langley, the data collected on crash-worthiness was deemed successful and just as important.

Findings

Post-impact 3

The actual impact demonstrated that the antimisting additive tested was not sufficient to prevent a post-crash fire in all circumstances, though the reduced intensity of the initial fire was attributed to the effect of AMK.[2]:20–22

FAA investigators estimated that 23% to 25% of the aircraft's full complement of 113 people could have survived the crash. Time from slideout to complete smoke obscuration for the forward cabin was five seconds; for the aft cabin, it was 20 seconds. Total time to evacuate was 15 and 33 seconds respectively, accounting for the time necessary to reach and open the doors and operate the slide. Investigators labeled their estimate of the ability to escape through dense smoke as "highly speculative".[2]:39–40

As a result of analysis of the crash, the FAA instituted new flammability standards for seat cushions requiring the use of fire-blocking layers, which performed better than conventional seat cushions in the resulting blaze[2]:33 They also implemented a standard requiring floor proximity lighting to be mechanically fastened, due to the apparent detachment of two types of adhesive-fastened emergency lights during the impact.[2]:38 Federal aviation regulations for flight data recorder sampling rates for pitch, roll and acceleration were found to be insufficient.[2]:39

NASA concluded that the impact piloting task was of an unusually high workload, which might have been reduced through the use of a heads-up display, the automation of more tasks, and a higher-resolution monitor. They also recommended the use of a microwave landing system to improve tracking accuracy over the standard ground radar provided by an instrument landing system (in practice, the GPS-based Wide Area Augmentation System came to fulfill this role).[1]:15-19

References

  1. ^ a b Horton, Timothy W.; Kempel, Robert W. (1988-11) (PDF), Flight Test Experience and Controlled Impact of a Remotely Piloted Jet Transport Aircraft, Edwards, CA, U.S.A.: NASA Ames Research Center, NASA-TM-4084, http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19890006539_1989006539.pdf, retrieved 2007-11-20, "The objectives of the CID program were (1) to demonstrate a reduction of postcrash fire through the use of antimisting fuel (Klueg, 1985), (2) to acquire transport crash structural data (Hayduk and Alfaro-Bou, 1985), and (3) to demonstrate the effectiveness of existing improved seat-restraint and cabin structural systems (Hayduk and Alfaro-Bou, 1985)."  
  2. ^ a b c d e (PDF) Full-Scale Transport Controlled Impact Demonstration Program, Atlantic City International Airport, NJ, U.S.A.: FAA Technical Center, 1987-09, DOT/FAA/CT-87/10, NASA-TM-89642, http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19880000639_1988000639.pdf, retrieved 2009-03-17, "This was the first time that a four-engine jet aircraft (Boeing 720) had been flown successfully by remote control. It was also the first time that an aircraft was flown solely and successfully on antimisting kerosene fuel (AMK)."  

Additional photographs and videos

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