Primary Flight Display

Pitch and Power: Lessons from Air France Flight 447

When the French BEA released a partial cockpit voice recorder (CVR) transcript of the Air France Flight 447 accident in late May, pundits wasted no time unleashing pointed analysis implicating the A330’s crew. The Airbus crashed into the South Atlantic, killing all 228 people aboard. Indeed, the edited details of the BEA seemed to offer few other possibilities. To some experts, however, the report actually raised more questions than it answered, leaving many to wonder about the BEA’s motivation in choosing the items it publicized.

Certainly the most telling element of the report was data indicating that not only did the pilot flying lose control of the airplane shortly after the autopilot and autothrottles disconnected on their own at 35,000 feet, but that while the aircraft was falling at some 11,000 fpm, he kept the sidestick pulled back, holding the 452,000-pound aircraft in a full stall. Air France received a series of automated messages before the crash that suggest the aircraft began shedding automation due to the loss of valid airspeed indications related to on-going icing issues with the Airbus’s Thales-made pitot tubes.

The brief BEA transcript reported that everything appeared normal in the flight until the moment the crew prepared to deviate around some forecast thunderstorms about four hours into the flight. Capt. Marc Dubois, the senior pilot aboard, had just left the cockpit for a required rest break and most likely transferred command of the aircraft to David Robert, who had 4,500 hours of experience in the A330. Pierre-Cédric Bonin, the most junior of the trio, had logged fewer than 3,000 hours total flying experience.

Just seconds after Air France Flight 447 began to deviate around the storms, the autopilot and autothrottles shut down as the aircraft rolled to the right. The pilot flying–believed to be Bonin–reacted by pulling back on the sidestick and raising the nose of the aircraft. The stall warning sounded twice as indicated airspeed on the captain’s primary flight display dropped quickly from 275 knots to 60 knots. The standby display showed the same numbers. About 10 seconds after equipment began failing, the microphone of the pilot not flying recorded, “We’ve lost airspeeds,” then “alternate law […]” most likely a reference to the system of Airbus control laws that determines which portions of the aircraft’s operating envelope the computers protect at any given moment.

aviation computers: Primary flight display [EN]

A primary flight display or PFD is a modern aircraft instrument dedicated to flight information. Much like multi-function displays, primary flight displays are built around an LCD or CRT display device. Representations of older six pack or "steam gauge" instruments are combined on one compact display, simplifying pilot workflow and streamlining cockpit layouts. While the PFD does not directly use the pitot-static system to physically display flight data, it still uses the system to make altitude, airspeed, vertical speed, and other measurements precisely using air pressure and barometric readings. An air data computer analyzes the information and displays it to the pilot in a readable format. A number of manufacturers produce PFDs, varying slightly in appearance and functionality, but the information is displayed to the pilot in a similar fashion. The details of the display layout on a primary flight display can vary enormously, depending on the aircraft, the aircraft's manufacturer, the specific model of PFD, certain settings chosen by the pilot, and various internal options that are selected by the aircraft's owner (i.e., an airline, in the case of a large airliner). However, the great majority of PFDs follow a similar layout convention. The center of the PFD usually contains an attitude indicator (AI), which gives the pilot information about the aircraft's pitch and roll characteristics, and the orientation of the aircraft with respect to the horizon. Unlike a traditional attitude indicator, however, the mechanical gyroscope is not contained within the panel itself, but is rather a separate device whose information is simply displayed on the PFD. The attitude indicator is designed to look very much like traditional mechanical AI's. Other information that may or may not appear on or about the attitude indicator can include the stall angle, a runway diagram, ILS localizer and glide-path “needles”, and so on. Unlike mechanical instruments, this information can be dynamically updated as required; the stall angle, for example, can be adjusted in real time to reflect the calculated critical angle of attack of the aircraft in its current configuration (airspeed, etc.). The PFD may also show an indicator of the aircraft's future path (over the next few seconds), as calculated by onboard computers, making it easier for pilots to anticipate aircraft movements and reactions.

Advanced Avionics Handbook

Instrument Flying Handbook

Controlling Pilot Error: Automation

Advanced Avionics Handbook

Change blindness in the synthetic vision primary flight display, comparing eye tracking patterns with pilot attention