Primary Flight Displays in the T-38C: When Do Differences Among Displays Become Inconsistencies

Abstract

and Guy A. FrenchAir Force Research LaboratoryWright-Patterson Air Force Base, Dayton OHThomas A. HitzemanFlight Training Systems Program OfficeWright-Patterson Air Force Base, Dayton OHIn the 1980s the US military settled on counterpointers, or dials, as the standard gauge for display of airspeed and altitude ina head-up display (HUD). This format is now making its way into production aircraft, one of which is the T-38C, a US AirForce (USAF) fighter jet trainer. The T-38C is unique in possessing three primary flight displays: a head-down primaryflight display (PFD) suite, a HUD in Military Standard (MIL-STD) emulation mode, and the same HUD in F-16 emulationmode. Differences among these displays include color, scale, and gauge format (e.g., tapes vs. dials). A study wasconducted as part of the Air Force’s primary flight display endorsement process to determine if differences among thesedisplays represent inconsistencies that might have practical impact on pilot performance, situation awareness, or workload.Sixteen T-38 pilots flew maneuvers designed to test spatial orientation and trend perception. Maneuvers were flown witheach PFD alone and in two transition conditions: from the MIL-STD HUD to the HDD, and from the F-16 HUD to theHDD. Flight performance data were collected and pilots also rated situation awareness (SA) and workload. Three seniorUSAF Instructor Pilots (IPs) graded each maneuver. No practically significant differences were found in performance:differences among conditions were small and not operationally relevant. Pilots actually rated SA higher and workloadlower when using the F-16 HUD, even though HUD and HDD gauge formats differed when using this display. Pilots alsorated the F-16 HUD higher than the MIL-STD for facilitating an efficient crosscheck, not presenting conflicting cues, andusing an intuitive data manipulation scheme. The results support a conclusion that consistency within a PFD is moreimportant than consistency across head-up and head-down PFDs: differences in location, color, and display medium mayfacilitate perceptual and attentional separation of the information displayed.IntroductionThe US military is now in its third generation of a Mili-tary Standard for primary flight symbology for HUDs(U.S. Department of Defense, 2000). A great deal ofwork has been done in generating this standard format(see Weinstein, Gillingham, & Ercoline, 1994) and thissymbology set is now finding its way into productionfighter/attack aircraft, including (with some modifica-tions) the F-22, the T-38C, and the F-35. Entering thelast decade of the 20th Century, the 1950s-era cockpitlayout and flight instruments of the USAF T-38A and T-38B fleets had fallen well behind the pace of technologi-cal change when compared to the integrated avionicssuites found in modern fighter and bomber aircraft, aswell as the new T-6A primary flight trainer. Avionics-related skills required in bomber-fighter (BF) aircraftwere not being taught or introduced in the T-38, and onlyone third of needed avionics-related skills and knowl-edge transferred from the T-38 to follow-on training.Follow-on BF training flight hours needed for weapons-system-specific training were instead being used to trainfundamental avionics skills.The basic flight characteristics and performance qualitiesof the T-38 remain well-suited for the BF Track andIntroduction to Fighter Fundamentals (IFF) training mis-sions. The T-38 Avionics Upgrade Program (AUP) in-corporates all-new digital avionics and electronic cockpitdisplays into a proven training airframe and engine com-bination. The AUP package, which changes the aircraftdesignation to T-38C, includes a head-up display and up-front controls, electronic head-down multi-function dis-play (HDD), hands on throttle and stick (HOTAS) con-trols, electronic engine displays, mission display com-puter, data transfer system, radar altimeter, and all newnavigation and communications systems. The T-38CAUP results in improvements to training viability andcapability and improved reliability.The next generation of USAF fighter and bomber pilotswill learn to fly HUDs in this unique trainer. One of thethings that makes this aircraft unique is that the cockpit(Figure 1) includes three PFDs. The first PFD (Figure 2)is a full-color set of instrumentation presented on oneHDD. Airspeed is presented on a single-turn dial with alogarithmic scale, attitude is presented via a standardADI (Attitude-Director Indicator) ball, altitude is pre-sented on a multi-turn dial with equidistant scale mark-ings and digital readout, and vertical velocity is presentedas a green arc with associated tic marks on the altimeter.The second PFD (Figure 3) is a monochrome HUD