If you’ve ever peeked into the cockpit while boarding a commercial flight, you might not have realized that the pilots are in the midst of one of their highest times of workload. Many tasks must be accomplished prior to pushing back from the gate, and it takes a great deal of coordination between the pilots, flight attendants, airline operations, and ATC to prepare for flight. In this article, I’ll walk through a typical sequence of events that leads up to your departure.
While you’re sitting at the gate waiting patiently to board, the pilots are in the process of powering up the aircraft. There are no keys, just the flip of a few switches to bring the aircraft to life. Usually the aircraft receives its power from an electric plug stemming from the jet-way until prior to pushback, upon which an onboard fuel-powered generator called an APU is used. Besides providing electrical power on the ground, the APU also delivers conditioned air to the cabin as well as high-pressure air to start the engines.
With the aircraft powered-up, the pilots run through a regimented sequence of systems checks to ensure both main and back-up systems are operating normally. Upon completion of these checks, flight crews read through a checklist to ensure that all tasks have been completed. The first officer reads the checklist aloud while the Captain responds with the appropriate response, such as “check”. Speaking of the first officer, they are generally the ones who perform an exterior pre-flight inspection ensuring the aircraft is fit for flight. If any problems are found, such as a tire needing air, the captain is notified to call the maintenance folks out to fix the problem.
Beyond those tasks, the pilots must also read through the flight plan that airline dispatch specialists prepare and upload to computers for printout. The flight plan includes important information such as fuel consumption data, route and altitude of flight, weather information, as well as airport remarks such as known taxiway and runway closures. The route of flight, altitudes to be flown, and fuel consumption data are entered by the pilots into an onboard computer called an FMS, or Flight Management System. This computer links the entered flight plan to the autopilot so that it can navigate the aircraft from point ‘A’ to point ‘B’. The fuel data entered allows the aircraft systems to track fuel burn during flight, providing the pilots with important information such as how much fuel will be onboard upon landing. For an example of the importance of this information, if ATC directs the pilots that airborne holding will be required, the expected holding time can be entered into the FMS and it will in turn calculate how long the aircraft can hold before needing to divert to re-fuel. Per FAA standards, aircraft are required to carry enough fuel for a given flight such that they can fly to their intended destination, proceed from there to an alternate airport, plus fly an additional 45 minutes beyond that. Any known ATC delays, such as anticipated holding must also be accounted for when planning fuel to be uploaded.
Once the FMS has been fed its required information, the pilots still have much to accomplish. About 30 minutes prior to push back, the flight crew either contacts by radio or receives an electronic message from ATC confirming their filed flight plan as well as assigning the flight a specific four number “squawk” code to enter into the aircraft transponder. The transponder is a device that automatically transmits a signal to ATC for radar tracking purposes. Every flight is given a unique squawk code that allows ATC to decipher each flight on their radar. Transponders also transmit signals between different aircraft, which allows pilots to track the position of other flights in the vicinity with an on-board display called a traffic collision avoidance system, or TCAS. This system will alert the pilots if another aircraft comes too close and will even go as far as to direct the pilots to climb or descend to avoid a collision if necessary. This of course is a back-up system to the services provided by ATC, but nonetheless is a valuable tool.
After the baggage has been loaded and the passengers are boarded, the pilots receive a baggage and passenger count. This information is then entered into the FMS for weight and balance calculations. With fuel, baggage, and passengers loaded, the total takeoff weight can be determined. This weight must not exceed the limitation of the aircrafts maximum allowable takeoff weight and also must allow for the aircraft to meet various runway and climb performance requirements. For example, there may be a weight limit for the runway being used that if exceeded, the aircraft may not be able to clear terrain or obstacles after takeoff in the event of an engine failure. Strict adherence to these weight limitations is crucial for a safe departure in the unlikely event of an emergency, or even during an uneventful flight. On the other side of the equation lies the balance issue. Airplanes are designed to be stable flying machines so long as they are loaded in a balanced fashion. If for example too much weight is loaded toward the rear of the aircraft, it would be tail-heavy and therefore would not handle appropriately. During balance calculations, the pilots may request that the flight attendants move passengers to different locations around the cabin to satisfy this requirement. The balancing issue is also important in setting the aircraft trim for takeoff. The trim, similar to the trim on a boat engine, assists the pilots by reducing the load they feel on the control yoke. Setting the trim properly for takeoff, based on aircraft balance, allows the aircraft to climb safely, especially in the event of an engine failure.
With these tasks completed, the seat belt sign is illuminated and the aircraft is ready to push off the gate. The pilots now shift their focus to preparing for takeoff and navigating you and your baggage safely to point ‘B’. Our pre-flight duties may seem like a daunting task, but I’d venture to say it’s easier than finding overhead bin space for your carry-on in most cases. Thanks for reading.