The anatomy of a commercial flight – all you ever wanted to know:   Part two   

In the previous installment of this two-part article, AeroTime took you through the initial stages of a routine commercial flight, from the pre-departure checks carried out by the pilots and cabin crew, to what is happening outside the aircraft, and from engine startup to taxi and take-off.  

With our aircraft now safely in the air and on the way to its destination, we can observe what is happening around us in the cabin as the crew go about their tasks. Meanwhile, up at the front of the plane, the pilots are monitoring their instruments and ensuring that the aircraft’s autopilot systems keep the plane on track.    

We will also examine the next most critical phase of our flight, from descent and deceleration to the approach and landing phases, even touching upon what happens when the aircraft arrives safely at the gate. So, remove your eyeshades, turn off the inflight entertainment screen in front of you, and take a moment to watch what is happening around you. Any flight you may take is always full of things to notice… 

Abdul Razak Latif / ShutterstockIn the cruise 

As you sit whiling away the hours until you reach your destination, there will still be many aspects of your flight to ponder. While the majority of your fellow passengers simply see their journey by air as a chance to ‘take off, eat, drink, sleep, land, disembark’, there is so much more to observe around you than simply staring at the back of the seat in front.  

We will start Part two of this article as your flight continues to cruise along. If you are an avid fan of watching the inflight moving map display and related data on your inflight entertainment screen, you may notice that, as your flight progresses, rather than descending or even staying at a fixed altitude, it may climb to a higher altitude. While this may appear strange, the economic logic behind it is quite straightforward.  

Jet (and turboprop) turbine engines work more efficiently, and burn less fuel, at higher altitudes where the air is less dense. Hence, the flight will use less fuel at higher altitudes. Additionally, as the flight progresses, the burning of fuel makes the aircraft lighter, which in turn means that it can climb more easily and takes less fuel to power along at higher altitudes. As such, aircraft – particularly those operating long-haul routes – will continually carry out stepped climbs throughout their journey to fly at the optimal height to maximize fuel efficiency at each stage. 

Miguel Lagoa / ShutterstockAs you look around at what is going on around you in the cabin, you may notice that certain rows of seats do not actually have a window assigned to them. But why is this, especially as those sitting nearest the cabin wall may have specifically requested or booked a window seat to gaze over the ever-changing landscapes below?    

Modern commercial airliners have complicated cabin air conditioning systems, as well as other electrical cabling and pipework that keep all the systems on the aircraft functioning. All of this hardware needs to be accommodated somewhere. While most of it tends to be hidden away either in the cabin ceiling space or under the cabin floor panels, some of it – particularly the air conditioning riser ducts – is fitted in the cabin walls at certain intervals, making the inclusion of a window at that position impossible.  

EQRoy / ShutterstockThis is a regular source of passenger frustration on certain airlines. Having been expecting to pass the hours away starring down at breathtaking vistas out of their assigned window, they are instead faced with a section of plastic wall paneling for what can be several hours. Although practically unavoidable, it is a quirk of modern air travel that few airlines disclose to their passengers at the time of booking. 

Speaking of cabin windows, people often notice that the window blinds on emergency exit row windows pull up to close, rather than the more conventional ‘pull-down’ style seen elsewhere on the aircraft. This again is a safety feature, but one which has traditionally been misinterpreted. While many believe that down-pull blinds are simply more susceptible to turbulence or heavy landings, making them more likely to simply drop down, there is an even more logical explanation than this. 

Corvin.Y.O / ShutterstockModern airliners have plug-style emergency exits that allow passengers seated in those rows to remove them and discard them outwards in the case of an emergency. However, as the design of these plug doors has evolved over the years, many – such as those found on Boeing 737 and Airbus A320 family aircraft – now have handles that allow the exit’s removal in case of an emergency.  

The existence of these handles, normally directly above the window itself, precludes a blind retracting into the wall space above the window. However, with aircraft types such as the Boeing 787 Dreamliner offering electrically operated window dimmers, the phenomenon of manual window blinds may soon become a thing of the past.  

Where did all the crew go?     

Having been up and down the aisles throughout the early stages of your flight, it is not uncommon, particularly on long-haul night flights, for the cabin crew to seemingly disappear, leaving just a skeleton crew of flight attendants to tend to the needs of the passengers. But where do all the other crew go to, and why?   

On medium and long-haul flights in particular, cabin crew are required by law to take regulated rest periods during their duty day, primarily so that fatigued crew members never compromise flight safety. Many widebody aircraft, and indeed some single-aisle aircraft, are equipped with specific locations so that crews can take rest periods out of the sight of passengers. These are collectively known as crew rest areas, and many passengers will never know they even exist, so discreetly hidden are they from those sitting in the cabin.

 

Maxene Huiyu / ShutterstockCrew rest areas provide a dedicated area in which crews can sleep, change, and have meals away from passengers. Depending on the type of aircraft involved, these areas can be located above the passenger cabin (such as the Boeing 777 and 787), at the rear of the main cabin up a small staircase (such as seen on the 747-400), or even on the lower deck in a Lower Deck Crew Rest Module (LDCRM) such as those featured on some Airbus A350s.  

On narrowbody aircraft, which generally tend to be used for short to medium-haul flights, some airlines will provide a curtained-off row (or two) of seats in which crew members can rest. Others simply expect crew members to sit on their jump seats in the rear galley area as they take their breaks and have their meals – hardly a restful environment.  

 

Jordan Tan / ShutterstockCabin lights and sounds 

While anyone familiar with air travel will instantly recognize the chimes or dings heard over the aircraft’s PA system (as referred to in Part One – ‘Ready for departure’), few will know what they all mean.  

The chimes – along with the use of different lights – provide a means for the cabin crew to communicate onboard. This is particularly important on larger, twin-aisle, and even twin-deck flights where the geography onboard makes it difficult for crews to communicate directly from one end of the aircraft to the other.  

At every cabin crew station, where crew members sit during take-off, landing, and during bouts of turbulence, interphones are available for cabin crew members to communicate with each other, as well as with the pilots on the flight deck. Of course, they also double up to act as the PA system for announcements to the passengers.  

KITTIKUN YOKSAP / ShutterstockDifferent chime signals are designated to mean different things and every cabin crew member is trained to identify each one. Used in combination with the chimes is a small strip of lights on each galley ceiling to notify crewmembers of different communications and where they are coming from, known as the Area Call Panel (ACP) or the Master Call Light panel (MCL). On Airbus aircraft, there is also the Attendant Indication Panel (AIP), which can provide additional information to the crew.   

The possible combinations of lights and chimes can convey a plethora of different information between the cabin crew stations. The lights can either stay on or flash, while the chimes can be low or high-pitched. Each combination of chimes and lights will have a different meaning, each one a different issue for the crew to deal with, but their meanings are largely withheld from the public domain for safety and security reasons. 

Purd77 / ShutterstockTop of descent 

With your aircraft typically around 45 minutes from its destination, it is routine for the pilots to make an announcement to the passengers over the PA system. This will generally convey information about the flight time remaining, the weather at the destination, and the flight crew thanking you for choosing their airline and wishing you “a safe onward journey” once on the ground.  

However, the real importance of this is that it gives the cabin crew notification of the remaining time available to clear away any remaining inflight catering items and to secure any loose items within the cabin for arrival.  It also marks the flight’s top-of-descent phase, before the actual descent comments towards the aircraft’s final destination.

Mario Hagen / ShutterstockThe announcement will also be one of the first items on the pilots’ before-descent checklist. After this list is completed, the aircraft will usually begin its initial descent from its cruising altitude toward its destination. This process is usually instigated by the flight crew, who will have used the aircraft’s flight management computer to calculate how many miles are left of the journey, as well as by which point the aircraft needs to begin its descent so that it doesn’t overshoot the airport at the end of its route. 

Depending on other traffic ahead, not least at the destination, air traffic controllers (ATC) will clear the flight to descend in stages, to be level at certain waypoints on the arrival route. This may be accompanied by the deployment of spoilers on top of the wing. These are upward hingeing panels that can assist the pilots in increasing the rate of descent without building up excessive speed. 

Jay Fog / ShutterstockAs the aircraft descends, it naturally wants to pick up speed; just think of a ball rolling down a hill. The flight crew deploys the spoilers on top of the wing to prevent the build-up of airspeed, particularly if a high rate of descent is required. With the deployment of the spoilers comes mild vibration throughout the airframe and additional noise as the disrupted airflow over the wings passes along the exterior of the passenger cabin. 

Approach and final descent 

As your aircraft nears the airport, the flight crew will be working hard to reach a certain speed and get the aircraft ready for landing. Having been cruising along at around 500 miles per hour (800 kph) or so, depending on aircraft type, the crew will need to reduce this to around 150 mph (240 kph) for the final approach, and even lower for the actual landing itself.   

The touchdown speed will have already been calculated using a combination of aircraft weight, length of runway in use, and prevailing conditions. In gusty conditions, for example, crews tend to add a few knots to their touchdown speed, which allows for fluctuations in airspeed while on final approach.  

At this point, the use of the aircraft’s flaps becomes critical. Flaps, which help to lower an aircraft’s speed while providing additional lift at those lower airspeeds, are lowered in stages, as adding too much flaps at once can upset the aerodynamics and thus stability of the aircraft. The lowering of the flaps in stages is prescribed by the aircraft operations manual, which will limit the amount of flaps that can be deployed at specific airspeeds. 

 

With the final stages of flap selected, the flight crew will lower the landing gear – an action that, although impossible to see from the cabin of a large jet aircraft, can nevertheless be audibly identified through the ‘whoosh’ sound as the main gear doors open and a ‘clunk’ sound as the gear legs lock into place.  

With the gear selected down and the flaps fully extended, the aircraft is all set for landing. If you are traveling towards the front of the cabin on an Airbus aircraft, you may also hear three ‘bleeps’ emanating from behind the flight deck door as the plane approaches the runway. On a Boeing aircraft, this sound will be three short warning horns. These noises denote the point at which the autopilot is disconnected by the handling pilot as they take over manual control to perform the landing. 

As the aircraft descends to the runway, the radio altimeter (a device that measures the aircraft’s height above the ground at low elevations) automatically calls out the height to go before touchdown, which allows the pilot handling to keep their eyes on the view of the runway ahead, rather than looking down at the instrument panel.

Thomas Roell / ShutterstockThe landing  

Once safely on the ground, you may notice that the spoilers have again popped up on top of the wing. Besides helping to slow the aircraft on approach, they can also be used to act as lift dumpers – effectively destroying (or ‘spoiling’) the lift created by the wing traveling through the air and forcing the aircraft onto the ground as the airspeed over the wing decays. The spoilers deploy automatically if selected to do so by the crew, once a critical proportion of the aircraft’s weight has settled on the main landing gear.    

You may also notice that upon landing, the engine sound increases for a short while. The flight crew may select reverse thrust, which acts as an additional braking system by deflecting accelerated air passing through the engine forwards, helping to slow the aircraft down to a manageable and safe taxi speed, enabling it to vacate the runway. The same applies to the selecting of reverse pitch on turboprop aircraft, which translates the thrust produced by the rotating propellor forwards creating a slowing effect.   

Once the aircraft has reached a safe taxiing speed at the runway turn-off point, the crew will guide the aircraft to its allocated parking stand. The wingtip strobe lights will be extinguished as the aircraft exits the active runway, while green taxiway centreline lights will be lit up by the control tower, guiding the aircraft to its parking stand.  

Upon reaching the stand, a ground-based marshaller may guide the aircraft to its final parking place using universally recognized hand signals. Alternatively, an aircraft parking and information system (APIS) can be used, by which a laser guidance system displays an arrow indicating the direction in which to steer, as well as closing rate and stopping guidance to the crew at the gate itself.

Once at the gate, the ground crew will insert chocks in front of and behind the aircraft’s wheels, the engine will be shut down, and finally, the red anticollision beacons will be turned off, signaling that it is now safe for all ground staff to approach the aircraft.  

Safely back on the ground 

Lastly, as you prepare to disembark, if you happen to have been flying on an Airbus aircraft, listen out for what is colloquially known in aviation circles as the ‘barking dog phenomenon’. This is when passengers may notice what seems to be the sound of a barking dog emanating from the cargo hold. This unmistakable sound can often be heard either as the plane prepares for pushback and engine start, or else on shutdown.  

Nature-Andy / ShutterstockThe source of this rather unconventional sound is a component known as the Power Transfer Unit (PTU). This part is an element of the aircraft’s hydraulic systems, located within the underfloor area in the center of the passenger cabin, and it facilitates the switching of electrical power from one system to another in the event of a failure. A PTU generally consists of a hydraulic pump connected to a hydraulic motor via a shaft. It performs its function by surging, which causes the component to repeatedly and suddenly spool up and down, resulting in the apparent ‘barking’ sound. 

Thanks for flying with us!  

Equipped with all the information contained within both parts of this article, you should now be able to board your next flight as an oracle of knowledge. You may even have a tick-list of things to look out for to pass the time as you head toward your destination, while also being ready to calm the nerves of any nervous flyers who may be seated around you and flinch at any unusual sights and sounds. 

There will undoubtedly be other sights and sounds that we have not covered in this article but rest assured that these are all routine. Just because you do not know what they are or what they may mean does not necessarily mean they are anything to be afraid of.  

Natee Meepian / ShutterstockFor the crew onboard your flight, all the above events are completely routine and simply form part of their working day. But should you see something that does trouble you, never be afraid to mention it to your cabin crew. After all, their primary concern is the safety of you and your fellow passengers.  

Now we have finally reached our destination, thank you for choosing to travel with AeroTime today, and we wish you a pleasant onward journey… 

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The anatomy of a commercial flight – all you ever wanted to know: Part one  

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