F-22 Raptor Gets Zapped by International Date Line The F-22 Raptor is one of the most advanced fighters in the world with its stealth capabilities, advanced radar, state of the art weapons. But in 2007, while on a 12 hour flight from Hickham AFB Hawaii to Kadena AFB Japan. The U.S. Air Force's mighty Raptor was zapped by the International Date Line (IDL).

The Problem The 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 pilots had NO instruments to fall back upon and were left literally in the dark.

The Problem - Decomposed A soft goal of the system was the accuracy of the Present Position Location. Erroneous Data from the FMS hurts the accuracy of the PPL. Malfunctioning Equipment or Flowed algorithms help make erroneous data.

FMS Typical Block Diagram in flight, a principal task of the FMS is to determine the aircraft's position and the accuracy of that position. The FMS accepts inputs from multiple sources, processes the input, and provides output data to the pilot’s Situational Awareness Display (SAD).

Situational Awareness Displays Present Position Location is extremely important to the pilot and is used as the pilot’s reference point.

WRSPM The Environment is simply the pilot strapped into the aircraft. The System is the Flight Management System, Navigation Database, Sensor Data; and the PPL and Local Time Algorithms. The Specification is what is known by both Environment and System. This is the SAD, Universal Time and WOW. WOW stands for Weight On Wheels and is visible to both the pilot and the software system. Basically, WOW is an indicator of whether the aircraft is on the ground or not.

Key Concepts & Algorithms 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 °) Time Zone = Longitude / 15 degrees If Longitude is East of the Prime Meridian, LT = UT + Time Zone If Longitude is West of the Prime Meridian, LT = UT – Time Zone

Case in point… IDL 179 ° E 1200z Monday Noon 179 ° W 1200z Sunday Noon Given: UT = 2400z Sunday midnight TZ = LON / 15° LT = UT + TZ LT = UT +/- (LON / 15°) Happy Day Scenarios: 157°W TZ= 157°W / 15° = 10W LT = 2400z - 1000z = 1400z Sunday 2:00pm 179°W TZ=179°W / 15° = 12W LT = 2400z - 1200z = 1200z Sunday noon 179°E 179°E / 15° = 12E LT = 2400z + 1200z = 1200z Monday noon Exception: 181°W TZ=181°W / 15° = 12W LT = 2400Z - 1200z = 1200z Sunday noon IDL 179 ° E 1200z Monday Noon 179 ° W 1200z Sunday Noon 157 ° W 1400z Sunday 2:00pm Using the Key Concepts and Algorithms, we may calculate Happy Day Scenarios and the Exception Case experienced by the Raptors. 181 ° W 1200z Sunday Noon

Recommendations… Do ensure your requirements are Testable Real Requirement: “The system shall process present position location accurately.” Do include qualified Standards and Principles in your Requirements Specification Avionics and Navigation Principles Key Concepts & Algorithms Avionics Standards DO-178C Software Considerations in Airborne Systems and Equipment Certification Avionics Regulatory and Advisory Agencies Federal Aviation Administration (FAA) Do NOT rely upon Tribal Knowledge. Unfortunately in my quest to find an example of a well written requirement for PPL, I was saddened to learn our Navigation Engineers use the requirement shown above. Do reference qualified Standards and Principles in your Requirements Specification. Example Avionics and Navigation Principals are the Key Concepts & Algorithms we just discussed. Example Avionics Standards are DO-178C and TS-C115c. If in doubt, you can always search your domain’s regulatory and advisory agencies.

The Solution - Decomposed All requirements must be testable to demonstrate that the software end product satisfies its requirements. To be testable, requirements must be specific, unambiguous, and quantitative whenever possible.

The Solution The solution is a safe and happy pilot.

Backup

F-22 Raptor Gets Zapped by International Date Line The F-22 Raptor is one of the most advanced fighters in the world with its stealth capabilities, advanced radar, state of the art weapons. But in 2007, while on a 12 hour flight from Hickham AFB Hawaii to Kadena AFB Japan. The U.S. Air Force's mighty Raptor was zapped by the International Date Line (IDL).

Problem The F-22 Raptor computer software failed when the aircraft crossed the International Date Line. IDL As the group of (6) Raptors crossed over the IDL, multiple computer systems crashed. Everything from fuel subsystems, to navigation and partial communications were completely taken completely offline. Numerous attempts were made to "reboot" the systems.

F-22 Glass Cockpit So, why was this a problem? The pilots had NO instruments to fall back upon and were left in the dark.

KC-10 saves the day! Luckily, there were no weather issues that day so visibility was not a problem. Also, the Raptors had their KC-10 refueling tankers to safely guide them home.

KC-10 Instrument Cockpit So, why didn’t the KC-10 refuelers experience a similar problem? The KC-10 cockpit uses the older instrument based technology.

Safely back home, the investigation begins… All six Raptors and their KC-10 refuelers landed safely back in Hawaii. Now the investigation begins into what went wrong.

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 1956 2007 1985 1884 1522 The International Date Line has confused explorers, navigators, and everyday travelers since humans began circumnavigating the globe nearly five centuries ago. A person who goes around the world from east to west (the same direction as the Raptors) would lose one hour for every 15° of longitude crossed, and would lose 24 hours for one circuit of the globe from east to west if they did not compensate by adding 24 hours when they crossed the IDL. As Magellan voyaged around the world, his failure to compensate for the IDL led him to arrive in Spain a day later than recorded. Many believe the IDL played a role in Amelia Earhart’s disappearance in 1937. In 1956 Hollywood popularized the IDL in the movie “Around the World in 80 days”. The pilot’s failure to compensate for the IDL led to the false conclusion he had lost the race. In 1985, the F-20 Tigershark’s navigation went haywire and the pilot had to fall back upon his compass. And in 2007, the F22 was zapped by the IDL. 1937

Inadequate requirements? The system shall calculate the aircraft’s present position latitude and longitude in degrees, minutes, and seconds. The system shall display the aircraft’s present position latitude and longitude in degrees, minutes, and seconds. Once in flight, a principal task of the FMS is to determine the aircraft's position and the accuracy of that position.

Overlooked corner cases? There are 360° of longitude (180° E to 180° W). The Greenwich Meridian represents 0 degrees E or W. The IDL represents 180 degrees E or W. There are 180° of latitude (90° N to 90°S)

Poorly developed code? Rapidly changing technology from analogue to digital flight controls Led to increasing software development Software Ada was mandated by government Difficult to find/hire Ada developers

Insufficient testing? Training by instrument and for operation. The simulator may or may not execute the target Flight Management Software.

Ready to fly, again. In the end, the engineers quickly corrected the software error and the F-22 was back in the air. This concludes my “as-is” presentation. For my “to-be” presentation, I will use the Requirements Engineering (RE) techniques we are learning in class to offer a solution which could have prevented the F-22 from being zapped by the International Dateline.