Every commercial flight is operated under a set of rules, either Part 121 or 135 (14 Combined Federal Regulation 121 or 135 [14 CFR 121 or 14 CFR 135]), that provide the legal requirements that the operator and crew must abide by throughout the pre-flight and operational segment of the flight.
One element, often times taken for granted – especially within the domestic Part 121 segment, is the flight planning portion of the pre-flight preparation. For the most part Part 121 domestic crews receive a dispatcher release, essentially the “paperwork,” that provides that max payload numbers, fuel requirements, filed flight-plan, route information, and an assortment of weather and Notice to Airmen (NOTAM) information that is used to program the on-board flight management system (FMS).
This input of information into the FMS is regularly verified against the listed paperwork and any errors found are promptly corrected, usually during the pre-departure crew briefing and prior to the BEFORE START checklist at most airlines. For the most part, and speaking from personal experience as a domestic 121 pilot, when flying to a familiar city from a familiar departure point, the fixes and flight plan remain the same as the last time, or the time before that, or the time before that time, or the time before that time before the first few times. In short, largely, the routings remain the same. Flying over the same route, over the same fixes, that we have done since day one. In some regards, you could say crews may become complacent and take the routing for granted considering that 1) a dispatcher utilized a computer system to develop the flight plan and 2) that an ATC facility provided a clearance, with any modifications, to the flight that authorizes them to operate along a set path.
Three parties, at the most basic level, have agreed to a certain flight path that the aircraft will utilize to depart and arrive at its destination. Here is but just one example. A revenue flight from Atlanta to Omaha, Nebraska. A simple check of flightaware.com produces a handful of flights, mostly operated by Delta airlines or Delta Connection partner ExpressJet Airlines with the following routing:
KATL COKEM7 CARPT BNA PLESS J45 STL LMN MARWI1 KOMA
KATL COKEM7 CARPT BNA PLESS J45 STL LMN MARWI1 KOMA
First, KATL and KOMA are simply the airport identifiers for Atlanta Hartsfield and Omaha’s Eppley airfield. Within the flightplan they merely represent the origination and termination points.
Next we have COKEM7, which represents a standard departure procedure used by aircraft departing Atlanta to the northwest. The utilization of standard departure procedures helps aid in enroute in-trail separation and helps keep the movement of aircraft from the departure corridor to the enroute phases in an organized manner. Most departure and enroute sectors prefer to have 10-15 miles of in-trail separation between two aircraft departing through the same departure “gate” or route.
After COKEM7 we have CARPT, BNA, and PLESS. These three represent fixes, or waypoints, that the flight will fly over. CARPTis actually the last fix on the COKEM7 departure. After CARPT, the flight progresses to BNA, a radio fix called a VOR. All VORs are identified by three letters, however they are also recognized by their name. In this instance, BNA is Nashville, TN. After BNA is PLESS that represents the fix on a recognized airway, J45 that runs SE to NW towards STL, another VOR representing St. Louis, MO. Departing STL, the flight continues to LMN, Lamoni, IA that transitions the flight onto theMARWI1 standard arrival route into Omaha Eppley Field.
Here is a graphical depiction of the flight path:
I provide this primer on flight routes due to my recent introduction to an accident that occur in 1979. Air New Zealand Flight 901 was a regularly scheduled “tourist” flight that departed Auckland, flew south to McMurdo Sound Antarctic before turning northbound to stop in Christchurch before returning to Auckland a day later.
Unfortunately, the 14th instance of Air New Zealand 901 would not return to Christchurch. Sadly all onboard were lost due to a controlled flight into terrain accident.
Chief among the contributing factors found during the investigative process was the programming of the computer flight plan, developed by Air New Zealand’s navigation department, that the crew was briefed on roughly two weeks prior to the flight. Additionally, this trip was the first for both the Captain and First Officer, both qualified to conduct the flight – however neither of them had actually performed the flight in the past. However, the flight briefing that occurred was customary for all crews who would conduct the flight and served as an indoctrination into the challenges that existed and built a basic foundation of familiarity with the flight route.
For the most part, due to the complacency that may develop, very few flight crews check the flight route presented to them in the dispatch paperwork against paper charts in Part 121 domestic operations. For most companies, this is no longer a required task for the flight crew considering the automation used by the dispatcher to develop the flight plan and Air Traffic Control’s approval or modification of said flight route. In the case of Air New Zealand 901, this proved to be an extremely fatal error. Unbeknownst to the flight crew, there was a typographical error that put the aircraft dangerously close to the primary sightseeing attraction, Mount Erebus on Ross Island. This error was in the formatting of a lattitude and longitude instrument fix that was programmed into the navigation system of the DC-10. The resulted formatting error produced a navigational error of approximately 25 miles, well off course of the previous flight paths normally used during the tourist flights. Previous flight paths took the aircraft south, into McMurdo Sound, well to the west of Mount Erebus and well clear of high terrain. This allowed the flight crews to, once in the sound and familiar with the visual conditions that were in place on each flight, an opportunity to navigate via visual reference around Ross Island to provide for a memorable experience for the passengers. The flight path in question for the accident flight brought the aircraft well left of McMurdo Sound, almost directly into the highest terrain areas on Ross Island, near the 12,500ft peak of Mount Erebus.
While this routing change only represents one element of the accident, this element highlights the role human factors has in the safe operation of any flying machine. More specifically, flying machines that depend on correct data entry from the crew. Which, additionally, requires accurate data provided by navigation specialist and dispatchers.
Contributing factors in the accident, official or not, was the crews belief that any altitude assignment provided by the American administered air traffic control facilities in McMurdo were safe to accept based merely off the belief that controllers would not allow an aircraft to descent to an unsafe altitude near terrain.
Sadly 277 individuals died due to an error that should have been detected by the final trapping mechanism – the flight crew. Perhaps, if at least one crew member on the flight deck had previous experience operating into the complex Antarctic environment they would have noticed the discrepancy (due to previous operational experience) and successfully adjusted to remain well clear of Mount Erebus.
Certainly flight planning has come a long way, at least in domestic Part 121 operations, that flight crews have a high confidence in the routing and work performed by their company’s respective dispatchers. However, flight crews must be cautioned to accept a routing that they are unfamiliar of without some level of check and cross-check of the route against current charts. Not only to verify the legitimacy of the routing, but to become familiar with any terrain along the route and potential diversion fields that are available should the need present itself. Additionally, when crews are going to operate into areas of high terrain or those that pose a significant operational risk, at least one crewmember on the flight deck has operational experience into the area – at least at most companies.
If you find yourself interested in learning more about the unfortunate loss of Air New Zealand Flight 901, I have to recommend the following series of YouTube videos. The clips that follow are from a documentary detailing the accident and the investigation that occurred shortly thereafter.
Thanks for reading. For those in the aviation industry, and specifically those with a safety background, what other accidents are you familiar with that were caused by incorrect route programming or failed cross-check? Stay safe out there – and always, always – check, cross-check, and check again.