My recent article “Preparing for Flight” was so well received that I’m inspired to shine light on yet another high-workload phase of flight – arrival and landing. As I mentioned in the previous piece, one of the highest times of workload for flight crews occurs at the gate prior to departure. This is a phase of preparation that sets the precedent for a successful flight. However, alongside the intensity of readying for departure, follows an equally demanding phase of arrival, landing, and taxi to the gate. Thorough coordination and communication between the flight crew and ATC, as well as proper follow-through in guiding the aircraft safely during descent and landing is crucial. I’ll initiate this topic from a point just prior to descent.
As the end of the en route phase of flight nears, pilots begin planning for arrival. Many of the busier airports filter arriving aircraft from all different directions by means of standardized arrival procedures. Each pilot carries with them navigation charts for every airport served by their respective airline, and included are all of the possible procedures that ATC may request to be flown. Each of these procedures has a name, for example, the PHLBO arrival procedure that guides aircraft from the southern U.S. into Newark’s Liberty Int’l airport. Not only do these arrival routes guide aircraft laterally to the airport area, but often they contain vertical guidance as well. On the PHLBO procedure for example, there are many points along the route that aircraft are required to cross at a certain altitude. These altitude assignments are called “crossing restrictions” and they help to ease the workload of ATC. Instead of having to instruct each specific aircraft to descend to different altitudes throughout the arrival, ATC can simply instruct pilots to “descend via the PHLBO arrival”. The pilots, aware of their arrival assignment before even leaving the gate, prepare for the arrival prior to initiating it. They will review the instructions of the arrival aloud to form a plan that conforms with the restrictions. The PHLBO arrival requires descending aircraft to meet multiple crossing restrictions. These altitudes are carefully chosen to separate PHLBO flights inbound to Newark from aircraft arriving and departing other airports in the area, such as Philadelphia Int’l, an airport directly underneath the final portion of the PHLBO arrival. The on-board flight management system (FMS) computer mentioned in my previous article is programmed by the pilots with the arrival as well as its many crossing restrictions and in turn directs the pilots via visual cues when to initiate descent to satisfy each altitude requirement. Pilots also use a mental formula as a back up to know when a descent must begin in order to arrive at a certain point at a certain altitude. For example, if a flight is cruising at 35,000’ and needs to cross a point at 25,000’, the altitude to lose is 10,000’. We drop off the last three zeros, leaving 10. This number is multiplied by three, based on a comfortable glide path of three degrees. Such a gradual descent allows your beverage to stay in place on its tray table. Anyway, 10 multiplied by 3 equals 30, which correlates to miles from the point to begin descent. So, 30 miles away we will begin our descent to meet the restriction - clear as mud right?
The first point at which descent begins is called the top-of-descent, or TOD. It’s around this time that we typically make our final passenger address sharing the current weather, estimated time of arrival, and gate of arrival. How do we know this information? Most commercial aircraft are equipped with an on board communications computer that pilots use to send and receive information from the airport or airline. Crews can request a weather report from most airports to be “e-mailed” to the flight deck. The current weather, runways in use, and pertinent airport notes such as taxiway closures are included in the message. A similar message is sent regarding arrival gate information. We even have the ability via this system to notify the airport folks, for example, if a customer will require a wheelchair upon arrival. This same system allows pilots to communicate with maintenance or dispatch should it be necessary while in flight. The FMS also generates an estimated time of arrival that we refer to in our passenger announcement. All of this computerized information is available by radio in the event of a computer failure.
As the aircraft nears the end of the arrival procedure, ATC then “vectors” aircraft for approach to the runway. Vectoring is a term given to the lateral directions provided by ATC. In terms of expected time, this is the most un-predictable phase of flight. If the airspace is quiet, ATC will more or less guide flights directly to the runway. On the other hand, if the skies are crowded, aircraft are often vectored all over the place, sometimes even away from the runway. ATC will furthermore issue speed reductions and lower altitudes as flights near the airport and one another. It comes down to arranging aircraft that are arriving from different directions into a single line-up to the runway. It’s organized chaos at times and what could be a 5-minute direct course to the runway can otherwise quickly become 30 minutes. The phrase “so close, yet so far” comes to mind in these situations! On clear nights, pilots can actually see the line up of aircraft in front of them as a trail of lights. Seeing this makes it almost predictable when ATC will instruct the next turn to commence to keep aligned in the queue.
Once aligned with the runway, pilots guide their aircraft for landing either visually or by means of an instrument approach. During times of low visibility, most runways are equipped with a system called an ILS (instrument landing system) that transmits signals to aircraft in order to guide them both laterally and vertically to the landing zone. These signals allow flight crews to follow on board instrumentation that guides them to a safe landing. The system is so accurate, that many aircraft are capable of landing with zero-visibility. In these cases, the autopilot will literally land the aircraft via the ILS guidance.
Taxiing to the gate after landing, believe it or not, is equally demanding to all previous phases. At busy airports, especially those with multiple runways being used at the same time, aircraft arrive, depart, and taxi within close proximity. ATC ground control carefully provides taxi instructions to pilots that are meant to keep them on a safe path to the gate. Flight crews and ATC alike must be extremely attentive during ground operations. In the interest of safety, new technologies have recently been introduced to help prevent incursions on the ground. ATC at many airports now has a display that depicts a real-time location of all aircraft on the ground. The system provide an alert if a collision course is detected.
Despite thorough planning and safe execution by your flight crews, a few frustrations will always be imminent. One such annoyance is having to wait for your arriving gate to become available upon landing. Finite gate space is a problem these days with so many scheduled flights. Airline operations does their best to arrange gate assignments based on availability for arriving flights, but if your flight is early, or an aircraft has a maintenance issue that delays its departure at your assigned gate, you’ll be waiting in most cases. As always, thanks for reading and keep a lookout for my bi-weekly contribution. (flightaware.com) More...