Identifying aircraft types by sound: the A320 whistle, MD-80 thunder and turboprop hum

You are at the spot, the camera is still in your bag, and from the direction of the approach comes a high, almost melodic howl. Experienced spotters often say “A320” before the aircraft even emerges from the haze. If you can identify aircraft types by sound, you have a real head start at the fence: you know earlier what is coming and have your camera up in time. This guide explains where the typical sounds come from – from the A320 family’s whistle through the hydraulic bark at the gate to the MD-80’s thunder and the turboprops’ hum – and where the limits of identifying by ear lie.

Identifying by sound: the short answer

An aircraft sound is made up of a few sources: the fan at the front of the engine, the exhaust jet at the back, the propellers on turboprops and the airflow around the airframe – that is, landing gear, flaps, slats and openings in the outer skin. Depending on the phase of flight, a different source dominates. On takeoff at high power, you mainly hear the engine and the jet. On approach the engines run almost at idle, so airframe noise comes to the fore – and that is exactly where the most famous type sound of all shows up, the whistle of the A320 family.

That is why a sound is a hint, not an identification. It narrows the choices, and you have to confirm with your eyes, binoculars or tracking. How to assign types visually with confidence is shown in the guide Identifying aircraft types for beginners.

The A320 whistle: a bottle tone under the wing

The high, rising and falling howl that many residents and spotters associate with the Airbus A320 family does not come from the engines. Its source is circular openings on the underside of the wings that are part of the fuel tank pressure relief. When air flows over these openings on approach, the air in the cavity behind them starts to vibrate – the same effect as blowing across an empty bottle. Because the engines deliver little thrust on final approach, this tone stands out clearly then.

The classic models A319, A320 and A321 are affected – that is, the types you see most often at German airports anyway. The solution is surprisingly small: a vortex generator in front of each opening swirls the flow so that a clean tone can no longer form. Airbus has delivered aircraft of the family with these parts since February 2014, and older aircraft can be retrofitted. The noise reduction on approach is given as up to 4 decibels. Lufthansa has also put A320s with vortex generators into service.

For you as a spotter, that means:

• A whistle heard strongly suggests an older, non-retrofitted aircraft of the A320ceo family.
• No whistle does not rule out an A320. An A320neo or A321neo is newer than the modification, and many ceo fleets are retrofitted.
• How to tell ceo and neo apart visually – by engine size, sharklets and other details – is explained in the article A320neo or ceo?.

The bark at the gate: the Power Transfer Unit

The second distinctive Airbus sound you hear not in the air but on the ground: a short, rhythmic bark that often shows up during engine start or after landing on the way to the parking position. Behind it is the A320 family’s Power Transfer Unit (PTU). It mechanically links two hydraulic systems so that one can supply pressure to the other without any hydraulic fluid being exchanged between them.

The PTU kicks in when a significant pressure difference arises between the systems. That typically happens when only one engine is running – when starting the first engine, during shutdown or when a crew taxis to the gate on one engine after landing. The unit’s rapid spooling up and down produces the barking sound. It is often better audible in the cabin than outside, but at observation decks close to the apron it reaches you too.

So if it barks on the apron, an A320 family jet is very likely nearby. It is of course not a reliable type feature in the sense of A319 versus A321 – for that you need the fuselage length and emergency exits, as described in the guide Telling the A318, A319, A320 and A321 apart.

The buzzsaw at takeoff: buzzsaw noise

When a jet with a large fan engine stands at the runway threshold and pushes the power up, you often hear a buzzing, sawing sound from the front or diagonally from the side. Spotters and engineers call it buzzsaw. It arises when the tips of the fan blades rotate faster than the speed of sound at takeoff power. Shock waves form at each blade tip, and because the blades are never exactly identical, the result is a mix of many individual tones that sounds like a saw.

You hear it on many turbofan jets, from a narrowbody like the Boeing 737-800 to a widebody on its takeoff roll. It is not a pure type feature, but a good hint at the generation: older jets with a small fan sound more like thunder and roaring on takeoff, modern large-fan jets more like a saw plus a rushing noise. Which engines hang on which type can be found in the guide Identifying engines.

Newer engines are quieter overall. One means to that end is the serrated trailing edges of the nacelle, the chevrons: they mix the exhaust jet more gently with the surrounding air. You find them, for example, on the Boeing 787-9 and on the Boeing 737 MAX 8. If a big twinjet strikes you as noticeably muted on takeoff, that is a sign of the new generation.

The MD-80 thunder: low bypass ratio

Anyone who has heard an MD-80 take off once does not forget the sound. The two rear-mounted Pratt & Whitney JT8D-200 engines produce a deep, rough roar that stands out from a long way off. The reason lies in the bypass ratio: in the -200 series, only about 1.7 times as much air flows around the core engine as through it. A large part of the thrust comes from a fast, hot exhaust jet – and jet noise rises very sharply with exit velocity.

And the -200 series is already the quieter development. The original JT8D, with a bypass ratio of about 1 to 1, powered the Boeing 727-200, the Boeing 737-200 and the DC-9, which were still considerably louder and in many places were only allowed to keep flying with hush-kit retrofits.

In Europe, the MD-80 family has practically disappeared from regular scheduled service as of October 2026. If you want to experience its sound live, you are mainly left with individual operators in the Americas and the occasional ferry or special flight. The type has lasted particularly long in Latin America, for example with Venezuelan airlines such as Laser Airlines. Before any plan, check whether the aircraft are actually still in service.

Its successor in spirit sounds quite different, the Boeing 717-200: it also has rear-mounted engines, but more modern turbofans with a higher bypass ratio – the same silhouette, but a much more civilized soundscape.

Sound	Typical cause	When you hear it	Points to
High, rising and falling whistle	Pressure relief openings under the wing	on approach, engines near idle	older, non-retrofitted A319/A320/A321
Short, rhythmic bark	Hydraulic Power Transfer Unit	on the ground during start, shutdown, taxiing on one engine	A320 family
Buzzing buzzsaw	Supersonic fan blade tips	during the takeoff roll, from the front or diagonally from the side	Turbofans with a large fan
Deep, rough roar	fast exhaust jet, low bypass ratio	on takeoff, often echoing for a long time	MD-80, 727, 737-200, DC-9
Steady hum or drone	Propeller blades	in all phases of flight, clear on approach	Turboprops like ATR, Dash 8, C-130, A400M
Loud rushing after touchdown	Thrust reversers	right after landing	Jets braking, not type-specific

Turboprops: hum instead of rush

Turboprops sound fundamentally different from jets. Instead of broadband rushing, you hear a rhythmic hum or drone whose fundamental tone depends on the number of propeller blades and their rotational speed: every blade that sweeps past produces a pressure pulse. More blades at the same speed therefore means a higher fundamental tone. On approach, when the propellers work with adjusted blade pitch, the tone often changes audibly – a hint you can listen for.

ATR 72 and ATR 42: The current versions such as the ATR 72-600 and ATR 42-600 fly with six-blade propellers, while the early ATR 72-200 still had four blades. You hear a peculiarity on the ground: in hotel mode, the right engine runs while a propeller brake holds the propeller fixed. The aircraft thus supplies itself with electricity and air conditioning. So if a rush comes from an ATR whose propeller is standing still, it is no ghost sound – and for you a reason to pay close attention to barriers on the apron.

Dash 8: The Dash 8-400 is faster and more powerfully engined than the ATR. Its PW150A engines turn large six-blade propellers, while the smaller Series 100 to 300 have four blades. How to tell the two families apart visually with confidence is shown in the guide Telling the ATR and Dash 8 apart.

Military turboprops: The classic Lockheed C-130 Hercules with four Allison T56 engines has a steady, penetrating drone that many spotters recognize immediately. The Airbus A400M carries eight blades per propeller, and the two propellers on each wing side turn against each other. Its sound seems deeper and more powerful than the Hercules’. If you hear both types more often, you quickly learn to tell them apart. You experience the A400M especially often at Wunstorf Air Base, the home base of the German A400M fleet – more in the article Plane spotting in Wunstorf.

Why sound can deceive

As useful as hearing is, it has limits you should know.

• Travel time of sound: Sound takes about three seconds to travel a kilometer. If you follow a sound with your eyes, you are looking behind the aircraft. Scan the sky a bit further ahead in the direction of flight.
• Doppler effect: An approaching aircraft sounds higher than one moving away. Especially with the whistle and the turboprop hum, you hear the tone drop as it passes overhead. That is physics, not a change of type.
• Wind and weather: With the wind, sound carries farther; against the wind, much less reaches you. Temperature layering, humidity and clouds also change how far and how long you hear a takeoff roll.
• Thrust setting and phase of flight: The same aircraft sounds completely different on takeoff at full power than on approach at idle thrust, while taxiing or with the auxiliary power unit running at the gate.
• Surroundings: Halls, terminals and noise barriers reflect sound back or shield it. At large airports, several aircraft also often overlap.

That is why a look at the runway direction in use is worthwhile: if you know which direction landings come from, you can assign approach sounds much better. The guide Flight tracking with ADS-B for spotters helps here, letting you check an auditory guess against real data in seconds.

How to train your hearing

Recognizing sounds is a matter of practice. With a simple routine, you learn more in a few spotting days than from any video.

For the fourth step, you will find everything on microphones, wind protection and levels in the article Recording engine sound. Good places to practice are spots with a view of takeoffs and landings at once, such as the Munich visitors’ hill or the Zeppelinheim viewing platform at Frankfurt Airport, where you hear lots of traffic of different types in a short time.

What to watch out for

• Pack hearing protection. Right at the runway threshold or next to a turboprop during engine start, it gets very loud. Especially if you stand at the fence for a long time, earplugs or earmuffs protect your most important tool for this topic.
• Do not infer the airline from the sound. The same A320 whistles at one airline and not at the next, depending on retrofit status. The sound says something about the technology, not about the operator.
• Focus on distinctive sounds. Whistling, barking, thundering and propeller hum are easy to tell apart. Subtleties between two modern large-fan jets, on the other hand, are hard even for experienced listeners.
• Never rely on hearing on the apron. A stationary propeller or a quiet auxiliary power unit does not mean that no engine is running. Always follow barriers and instructions.

Conclusion

Identifying aircraft by sound is no magic, just applied technology. The older A320 family’s whistle comes from openings under the wing, the bark at the gate from the hydraulics, the buzzsaw on takeoff from supersonic flow at the fan blades and the MD-80’s thunder from its fast exhaust jet. Turboprops give themselves away with their hum, and with a bit of practice you can even tell the Hercules and the A400M apart. Hearing is your early warning system – in the end, identification is done with the eyes.