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In the interest of further increasing safety in the commercial airplane industry, the U.S. Federal Aviation Administration has effected a rule change that increases the amount of flight information collected in flight data recorders (FDR). The ability to gather additional information after a commercial airplane accident or incident can result in a more thorough investigation, as well as help the industry identify trends and make necessary modifications to prevent future accidents and incidents. Boeing is offering operators the support they need to meet the requirements of the new FAA rule by the date of compliance. ("Performance Data for European Operators" in the January-March 1997 issue of Airliner magazine addresses the rule for operators of JAA-registered airplanes.) The following article discusses:

1. Purpose of flight data recorders.
2. History of flight data recorders.
3. Summary and effects of the flight data recorder rule change.
4. Boeing support for operator compliance.

The purpose of an airplane flight data recorder system is to collect and record data from a variety of airplane sensors onto a medium designed to survive an accident. Depending on the age of an airplane, the FDR system may consist of (1) an analog or digital flight data acquisition unit (FDAU) and a digital FDR (DFDR) that may have a tape or solid-state memory, or (2) simply an FDR. The protected medium that collects data from an airplane resides in the FDR or DFDR. This recording system has been installed in thousands of airplanes, and continues to play a key role in making airplane travel as safe as possible.

The data collected in the FDR system can help investigators determine whether an accident was caused by pilot error, by an external event (such as windshear), or by an airplane system problem. Over the years, these data have contributed to airplane system design improvements and the ability to predict potential difficulties as airplanes age. An example of the latter is using FDR data to monitor the condition of a high-hours engine. Evaluating the data could be useful in making a decision to replace the engine before a failure occurs.

Flight data recorders were first introduced in the 1950s. Many first-generation FDRs used metal foil as the recording medium, with each single strip of foil capable of recording 200 to 400 hr of data. This metal foil was housed in a crash- survivable box installed in the aft end of an airplane. Beginning in 1965, FDRs (commonly known as "black boxes") were required to be painted bright orange or bright yellow, making them easier to locate at a crash site.

Second-generation FDRs were introduced in the 1970s as the requirement to record more data increased, but they were unable to process the larger amounts of incoming sensor data. The solution was development of the flight data acquisition unit (FDAU).

As shown in figure 1, the FDAU processes sensor data, then digitizes and formats it for transmission to the FDR. The second-generation digital FDR (DFDR) uses tape similar to audio recording tape. The tape is 300 to 500 ft long and can record up to 25 hr of data. It is stored in a cassette device mounted in a crash-protected enclosure.

FAA rule changes in the late 1980s required the first-generation FDRs to be replaced with digital recorders. Many of the older FDRs were replaced with second-generation magnetic tape recorders that can process incoming data without an FDAU. Most of these DFDRs can process up to 18 input parameters (signals). This requirement was based upon an airplane with four engines and a requirement to record 11 operational parameters for up to 25 hours (see "Parameters Explained").

Another FAA rule change that took effect October 11, 1991, led to the installation of digital FDAUs (DFDAUs) and DFDRs with solid-state memory on all Boeing airplanes before delivery. This FDR system was required to record a minimum of 34 parameter groups. The DFDAU processes approximately 100 different sensor signals per second for transmission to the DFDR, which uses electronics to accommodate data for a 25-hr period.

Cut-away view Today all Boeing current-production models use DFDR systems, which will store 64 12-bit words per second (wps) over a 25-hr period in electronic memory. At the end of the 25 hours, the DFDR will begin recording the most recent data over the oldest data. No tape removal is required with these systems. Each of these systems on every Boeing model (except the 777) have at least two data frames that are transmitted from the DFDAU to the DFDR (see "What Is a Data Frame?").

These separate data frames accommodate the different regulatory agency requirements. A 128-wps DFDR was available for the Boeing 777 and MD-90, allowing the development of one data frame that incorporated all regulatory agency requirements and that required operators to develop only one data frame decode algorithm. "How an FAA Rule Is Changed" explains the basis on which the FAA may propose rule changes.

The rule change addresses all Boeing commercial airplane models and groups them as follows:

Airplanes manufactured before October 11, 1991, without an FDAU or DFDAU as of July 16, 1996.
Airplanes manufactured before October 11, 1991, with an FDAU or DFDAU as of July 16, 1996.
Airplanes manufactured after October 11, 1991, after August 18, 2000, and after August 18, 2002.

Airplanes manufactured prior to october 11, 1991, without an FDAU or DFDAU installed as of July 16, 1996.
The new rule requires that by August 18, 2001 the FDR record at least 18 parameter groups. For most airplanes, this is an increase from 11 parameter groups, as described in "Effects of 1989 FAA Flight Data Recorder Rule Change" on page 32. On about half of all the Boeing 727, 737, DC-8, and DC-9 models the FDR system uses a single FDR, a result of the late 1980s replacement activity. Most of these FDRs should have enough spare inputs to accommodate the increased requirements with little or no modification required. Other parameter groups required to be recorded include the addition of both flight control surface positions and flight control inputs for all three axes (lateral, directional, longitudinal), lateral acceleration, and autopilot engagement status.

Airplanes manufactured prior to October 11, 1991, with a FDAU or DFDAU installed as of July 16, 1996.
The new rule requires that by four years from date of rule at least 22 parameter groups be recorded by the FDR. In this group are Boeing models 727, 737, 747, 757, 767, DC-10, and MD-80. Most of these airplanes record almost all the 22 parameter groups, some of which operators may ask Boeing to remove to save weight or to avoid maintenance costs if a parameter group is not required by a particular country's regulatory agency. The additional parameter groups required to be recorded include the addition of flight control surface positions and flight control inputs for all three axes, lateral acceleration, and autopilot engagement status.

Airplanes manufactured after October 11, 1991.
The 34 required parameter groups for this category are all recorded, with a few exceptions (some of the required recording rates are not met for flight control surface positions, flight control inputs, or both). The rule gives operators until August 18, 2001, to comply. Since the rule became effective August 18, 1997, the FDR system changes required for airplanes manufactured after August 18, 2000, will affect only new production. The new-production part of the rule changes require 57 parameter groups to be recorded by August 18, 2001, and 88 parameter groups by August 18, 2002.

Boeing models 707, 727, 737-100/-200/-300/-400/-500, 757, 767, 747-100/-200/-300/-400, 777-200/-300, DC-8, DC-9, DC-10, MD-11, MD-80, and MD-90 will require retrofit activity. This may involve the addition of new sensors and wiring plus installation of a DFDAU, software, or both because of a new FDR frame. The details of the Boeing plan to support the airplanes listed below are discussed in "Rule Change Support Plan".

The following airplanes are covered by the rule change support plan:

717-200.
727 and 737-100/-200 (all manufactured before October 11, 1991), 737-100/-200, and 737-300/-400/-500 manufactured before October 11, 1991.
737-300/-400/-500 manufactured after October 11, 1991, but before August 18, 2000 (production cut-in of 57/88 parameter groups).
737-600/-700/-800.
747-100/-200/-300.
747-400s manufactured before August 18, 2000 (production cut-in of 57/88 parameter groups).
757s and 767s manufactured before October 11, 1991.
757s and 767s manufactured before August 18, 2000 (production cut-in of 57/88 parameter groups).
777s manufactured before August 18, 2000 (production cut-in of 57/88 parameter groups).
All current-production Boeing models.
Airplanes that require 18 to 22 parameter groups and whose data frames will be affected.
747-400 and 777.
DC-8, DC-9, and 707 (all manufactured before October 11, 1991).
DC-10 (all manufactured before October 11, 1991) and MD-80 (with FDAU) manufactured before August 18, 2000 (production cut-in of 57/88 parameter groups).
MD-11, MD-80, and MD-90 manufactured before August 18, 2000 (production cut-in of 57/88 parameter groups).

Summary
The FDR rule change effected by the FAA in late 1997 will require operators of airplanes flying under FAA rules to make sure the FDRs on their airplanes can record several additional parameter groups. The compliance date for these airplanes depends on their date of manufacture. Boeing is ready to support all customers with their activities to meet the new FDR rule. Operators should contact Boeing to initiate a customer requested change if their airplanes need additional sensor and bracket installations but are not covered in the service bulletins that Boeing offers. Though Boeing has no plans to provide unique FDR data frame updates for airplanes manufactured before October 11, 1991, the company will respond to requests for assistance if an operator generates a customer change request.