F-22 Raptor Gets Zapped by International Date Line

The ProblemThe Flight Management System (FMS) failed to properly process the Present Position Location (PPL) as the F-22 Raptors crossed over the International Date Line. As a result, systems dependent upon accurate PPL failed…

The Problem

The Problem - Decomposed

FMS Typical Block Diagram

Situational Awareness Displays

WRSPM

Key Concepts & Algorithms

Key Concepts

• Two important concepts, related to Longitude (LON) are Local time (LT) and Universal Time (UT)

• Longitude determines the hour of the day--not the date.

• The International Date Line (IDL) determines the date. As we cross the IDL the date advances one day (going west) or goes back one day (going east).

• Universal Time (UT) or GMT is the Standard used for Aviation.

• The Earth is divided into (24) Time Zones. Each Time Zone (TZ) is 15° wide.

Algorithms

TZ = LON / 15 °LT = UT +/- TZ LT = UT +/- (LON / 15 °)

Case in point…Given: UT = 2400z Sunday midnight

TZ = LON / 15°LT = UT + TZ LT = UT +/- (LON / 15°)

Happy Day Scenarios:

157°W TZ= 157°W / 15° = 10WLT = 2400z - 1000z = 1400z Sunday 2:00pm

179°W TZ=179°W / 15° = 12WLT = 2400z - 1200z = 1200z Sunday noon

179°E 179°E / 15° = 12ELT = 2400z + 1200z = 1200z Monday noon

Exception:

181°W TZ=181°W / 15° = 12WLT = 2400Z - 1200z = 1200z Sunday noon

IDL

157 ° W1400z Sunday 2:00pm

179 ° W1200zSunday Noon

179 ° E1200zMondayNoon

181 ° W1200zSundayNoon

Recommendations…• Do ensure your requirements are Testable

o Real Requirement: “The system shall process present position location accurately.”

• Do include qualified Standards and Principles in your Requirements Specificationo Avionics and Navigation Principles

• Key Concepts & Algorithms o Avionics Standards

• DO-178C Software Considerations in Airborne Systems and Equipment Certification

o Avionics Regulatory and Advisory Agencies• Federal Aviation Administration (FAA)

The Solution - Decomposed

The Solution

Backup

F-22 Raptor Gets Zapped by International Date Line

Problem• The F-22 Raptor computer software failed when

the aircraft crossed the International Date Line.

IDL

F-22 Glass Cockpit

KC-10 saves the day!

KC-10 Instrument Cockpit

Safely back home, the investigation

begins…

What went wrong?• The Flight Management System failed to properly

process the location data as the F-22 flew from Hickam AFB (157° W) and crossed over the International Date Line (both 180° W and 180° E).

International Date Line

2007

1522

1937

1985

1956

1884

Inadequate requirements?

o The system shall calculate the aircraft’s present position latitude and longitude in degrees, minutes, and seconds.

o The system shall display the aircraft’s present position latitude and longitude in degrees, minutes, and seconds.

Overlooked corner cases?

Poorly developed code?

• Rapidly changing technology from analogue to digital flight controlso Led to increasing software

development

• Software o Ada was mandated by governmento Difficult to find/hire Ada

developers

Insufficient testing?

Ready to fly, again.