Electrical transmission or interconnection systems – Plural supply circuits or sources – Substitute or emergency source
Reexamination Certificate
2000-05-26
2002-06-25
Fleming, Fritz (Department: 2836)
Electrical transmission or interconnection systems
Plural supply circuits or sources
Substitute or emergency source
C307S085000
Reexamination Certificate
active
06410995
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The invention relates generally to avionics equipment, such as flight recorders. More particularly, the invention relates to a back up power supply for avionics equipment that can be installed in existing equipment trays located for example, but not exclusively, in the tail section of an aircraft, without having to rewire the aircraft.
2. State of the Art
The state-of-the-art is best introduced with the excerpts and paraphrases from the National Transportation Safety Board, Safety Recommendation A-99-16-18, dated Mar. 9, 1999.
Although the recommendations set forth hereinafter are directed to back up power supplies for cockpit voice recorders (CVR's) per se; those skilled in the art will readily appreciate that back up power supplies may be useful to power other types of avionics equipment should power from the aircraft's power supply be lost. Hence reference hereinafter to CVR's is intended for illustrative purposes only; and not to limit the scope of the invention described and claimed herein.
Many recent aircraft accidents have illustrated the need for an “independent” back-up power supply for the aircraft CVR. As used herein, the word “independent” means independent from the aircraft power supply, not necessarily independent from the CVR unit.
For example, on May 11, 1996, the crew of ValuJet flight 592, a DC-9-32, reported smoke and fire shortly after departing Miami, Fla. The flight recorders stopped about 40 to 50 seconds before the airplane crashed on its return to the airport.
On Jul. 7, 1996, TWA flight 800, a Boeing 747-100, on an international passenger flight from New York to Paris, exploded about 13 minutes after takeoff as it was climbing through 13,700 feet. Both flight recorders stopped at the time of the explosion, but the airplane did not hit the water off Long Island, N.Y., for another 40 to 50 seconds.
On Dec. 19, 1997, SilkAir flight 185, a Boeing 737, entered a rapid descent from 35,000 feet, which ended with a high speed impact in the Sumatran River near Palembang, Indonesia. The Indonesian investigation determined that both flight recorders stopped prior to the airplane entering the rapid descent.
On Sep. 2, 1998, Swissair flight 111, an MD11, on a regularly scheduled passenger flight from New York to Geneva, Switzerland, diverted to Halifax after the crew reported smoke in the cockpit; the airplane crashed into the waters near Peggy's Cove, Nova Scotia. Thus far, the Canadian Transportation Safety Board's (TSB) investigation has been severely hampered by the lack of data from the cockpit voice recorder (CVR), which stopped nearly 6 minutes before the airplane hit the water.
These recent accidents are just the latest in a long history of accident and incident investigations that were hindered by the loss of flight recorder data due to the interruption of aircraft electrical power.
Since 1983, the origin date of the NTSB database, there have been 52 accidents and incidents, including the 4 recent accidents mentioned above, in which information from either a CVR or FDR (flight data recorder) or both were lost due to interruption of electrical power following an engine or generator failure or crew action. Until recently, recorder technology did not offer a practical solution to the problem of loss of electrical power to the on-board recorders. However, recent innovations in recorder and power supply technologies have made it possible to provide an independent power source that would provide sufficient power to operate a solid-state flight recorder for a predetermined period of time, for example, 10 minutes.
In assessing the feasibility of an independent power source, strong consideration must be given to reliability, complexity, maintainability, and cost. The independent power source must also automatically engage when power to the recorders is lost; and disengage after a predetermined period of time so as not to overwrite recorded data.
Older model tape-based recorders require too much electrical power and are not easily adapted to a direct current (d.c.) battery or capacitor. However, the relatively low power requirements of solid-state flight recorders (about 10 to 12 watts from a 28-volt d.c. system) would permit the use of an independent power source. Thus, it is evident that the use of an independent power source would also require the use of solid-state flight recorders.
Current regulations call for a CVR with a minimum 30-minute recording duration. This minimum requirement was based on the limitations of 1960s recorder technology, which was constrained by the amount of magnetic tape that could be impact/fire protected.
In the years since CVRs became mandatory, the Safety Board has investigated many accidents and incidents for which the 30-minute CVR recording was not sufficient to retain key events. This prompted the Safety Board to recommend in 1996 that all newly manufactured CVRs be SSCVRs (solid state CVRs) with a 2-hour recording duration (Safety Recommendation A-96-171). Accident investigations in which the Safety Board has participated subsequent to the issuance of Safety Recommendation A-96-171 continue to demonstrate that a lack of recorded voice and other aural information can inhibit safety investigators and delay or prevent the identification of safety deficiencies.
The CVR installed on Swissair flight 111 used a continuous-loop magnetic tape with a 30-minute duration. The earliest information on the CVR tape was recorded about 15 minutes before the crew noted an unusual odor. Crew conversations and cockpit sounds prior to the beginning of this 30-minute recording might have provided insight into any initiating or precursory events that led to the accident.
About 38 minutes prior to the crew noting an unusual odor, Boston Center issued flight 111 a radio frequency change. During the following 13 minutes, Boston Center made repeated attempts to contact flight 111 but did not establish contact. Any cockpit conversations, flight deck noises, or attempted crew transmissions that occurred during this period were subsequently overwritten on the CVR, and thus were not available to the accident investigators.
Although 30-minute magnetic tape CVRs are no longer being manufactured, units still exist and could be installed on aircraft today. Given the continued need for longer periods of recorded sound to capture the initiating events of aviation accidents, and the availability of and trend toward 2-hour CVRs, the Safety Board has stated that a retrofit program is warranted.
The Safety Board has further stated that the Federal Aviation Administration (FAA) should require the retrofit after Jan. 1, 2005, of all CVRs on all airplanes required to carry both a CVR and a FDR with a CVR that meets TSO C123a and is capable of recording the last 2 hours of audio.
A number of options have been identified for realizing an independent power source. In assessing the feasibility of these options, batteries and capacitors appear to be the most effective means of providing aircraft independent power. These and other power sources may be selected by those skilled in the art based on various well known design criteria and objectives. For example, the capacitor method would provide a power source that requires very little maintenance when compared with a rechargeable battery since, unlike a rechargeable battery, the capacitor method would not require any power sensing circuitry for normal operation. Nevertheless, total package weight, center of gravity, packaging constraints (dimensional), etc., will all factor in when selecting among the possible candidates for an independent power supply.
To maximize recorder reliability and to minimize any crew intervention, the independent power source should automatically engage whenever the normal electrical power to the recorder ceases, even when the aircraft is powered down normally. To increase the probability of recording accident data, the independent power source should be capable of powering the recorder for 10 minutes after main power to
Dismukes Mart D.
Grouse Charles J.
Purdom Gregory W.
Fleming Fritz
Kaliko Joseph J.
L-3 Communications Corporation
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