How to tell the Boeing 737 Original, Classic, NG and MAX apart

Shortly before touchdown a 737 slides into the frame – but which one? Hardly any airliner has been in production as long as Boeing’s short-haul bestseller, and hardly any looks so similar over the decades. Fuselage cross-section, nose and basic shape have been essentially the same since 1967. Still, you can reliably tell the Boeing 737 Original, Classic, NG and MAX apart if you know where to look. This guide shows you the features that work from the fence: engine nacelle, wingtip, tail, tail cone and doors.

The short answer

Look first at the engine, then at the wingtip, last at the tail. Slim, long engine tubes directly under the wing belong to the Original generation. Fat nacelles with a flattened underside that sit ahead of the wing are found on Classic and NG. If the nacelle has a serrated edge at the trailing edge and the tail tapers out long and pointed, it is a MAX. You separate Classic and NG at the wing: the NG has a clearly larger wingspan, a taller vertical stabilizer and mostly winglets.

The four generations at a glance

Before getting into the details, a look at the timeline helps. Each generation brought new engines, and those shape the appearance most strongly.

• Original (737-100 and -200): The 737-100 first flew on April 9, 1967, with Lufthansa as launch customer. Only 30 examples were built. The stretched 737-200 became the real success and stayed in production until 1988. Both are powered by Pratt & Whitney JT8D – slim engines with a low bypass ratio.
• Classic (737-300, -400, -500): With the 737-300, first flight in February 1984, Boeing switched to the CFM56-3. The stretched 737-400 and the short 737-500 followed. The last Classics were delivered in 2000, almost 2,000 in total.
• Next Generation (737-600 to -900ER): The NG came in the late nineties with a new wing and CFM56-7 engines. The 737-700 flew first in February 1997, the 737-800 followed in July 1997 – launch customer of the -800 was, by the way, the German Hapag-Lloyd. Added to these are the small 737-600, the 737-900 and the 737-900ER. Passenger NGs were delivered until early 2020.
• MAX (MAX 7, 8, 9, 10 and 8-200): The MAX first flew on January 29, 2016, and entered scheduled service in May 2017. It carries the CFM LEAP-1B. After two crashes the fleet was grounded worldwide in March 2019; the US Federal Aviation Administration (FAA) lifted the grounding in November 2020, EASA in early 2021. The MAX 8 is by far the most common variant, alongside the MAX 7, MAX 9, MAX 10 and the 737-8-200.

If you want to dig deeper into the manufacturer’s background, the profile of Boeing places the 737 in the whole program.

Feature 1: The engine nacelle

No feature separates the generations as clearly as the engine. The 737 sits very low to the ground by design – originally so that baggage and stairs work even at small airports without much equipment. Every new engine generation therefore had to be squeezed somehow under the wing, and you can see exactly that.

Original: The JT8D engines are long, slim tubes that reach almost across the whole wing chord and hang directly under the wing. From the side they look like cigars that extend rearward beyond the trailing edge of the wing. A thrust reverser at the end of the tube is typical.

Classic and NG: The CFM56 engines have a much larger fan. To fit at all, they sit ahead of the wing instead of under it, and Boeing moved the accessory gearbox from the bottom to the side. The result is the famous flattened air inlet, often called “hamster cheek” among spotters. The NG’s nacelle (CFM56-7) is slightly longer and looks more powerful than the Classic’s (CFM56-3), but while it rolls past that is hard to see without practice.

MAX: At around 1.76 meters, the LEAP-1B has a clearly larger fan than the NG’s CFM56-7 at about 1.55 meters. The nacelle sits even further forward and higher on the wing, and Boeing lengthened the nose gear by about 20 centimeters to maintain ground clearance. The surest identifier, though, is the chevrons: the trailing edge of the nacelle is serrated like a saw blade – a noise reduction measure you also know from the Boeing 787.

Generation	Engine	Nacelle shape	Position relative to the wing
Original (-100/-200)	Pratt & Whitney JT8D	long, slim, round	directly under the wing, reaches far back
Classic (-300/-400/-500)	CFM56-3	fat, flattened at the bottom	ahead of the wing
NG (-600 to -900ER)	CFM56-7	fat, flattened at the bottom, slightly longer	ahead of the wing
MAX	CFM LEAP-1B	larger, with serrated trailing edge	further forward and higher

How to tell engines apart in general is shown by the guide Recognizing engines. You will find more on the manufacturer of the CFM56 and LEAP family at CFM International.

Feature 2: Wing and wingtips

The wing mainly separates Classic and NG. For the Next Generation Boeing redesigned the wing: it is around 4.9 meters wider, has about a quarter more area and a thinner profile with a larger chord. In comparison the Classic therefore looks stubby and short-winged, the NG by contrast stretched.

For wingtips there are four looks you should know:

• No winglets: Typical for Original and Classic, but also for the 737-600 and some -700s and -800s. A wing without a winglet is therefore no sure sign of an old aircraft.
• Blended winglets: Large winglets curving softly upward out of the wing. They are widespread on the NG and were also offered by Aviation Partners Boeing as a retrofit for the Classic types -300 and -500. A Classic with winglets nevertheless remains a rarity.
• Split Scimitar: Offered for NG variants from 2014. The blended winglet gets a sharply cut tip and an additional downward-pointing spur.
• MAX winglet: The MAX carries its own Advanced Technology winglet with one part pointing up and one pointing down. It is drawn tighter than the NG’s retrofit solution but resembles it.

Exactly at this point most mix-ups happen: an NG with Split Scimitar and a MAX look very similar from below at first glance. Never rely on the wingtip alone. More on the shapes is in the guide Winglets, sharklets, Split Scimitar and raked wingtips.

Feature 3: Vertical stabilizer and tail cone

The tail is the second-best feature after the engine – and it helps exactly where winglets mislead.

Vertical stabilizer: On the Classic, Boeing reworked the vertical stabilizer with a dorsal fin at the transition to the fuselage. For the NG it was redesigned again and is visibly taller. If a Classic and an NG stand side by side at the gate, the difference in height strikes you immediately; on their own it takes a little practice.

Tail cone: On Original, Classic and NG the fuselage ends relatively bluntly at the rear, with the clearly visible exhaust opening of the auxiliary power unit (APU). On the MAX, Boeing reshaped the tail cone: it tapers out longer and ends more pointed. Once you have seen an NG and a MAX one after the other on the taxiway, you recognize the difference almost in passing afterward.

Feature 4: Cockpit windows and nose

The 737’s nose has hardly changed across all generations – that makes it a sure feature against Airbus, but not between the generations. One detail helps anyway: the so-called eyebrow windows, small additional windows above the main panes. Original and Classic generally have them. On the NG they were left out over the course of production, and on many older aircraft they are plated over or still present. The MAX does not have them. If the windows are missing, that only largely rules out Original and Classic; if they are there, a lot speaks against a MAX.

How to infer a type from nose and windows in general is explained by the guide Recognizing aircraft types by nose and cockpit windows.

Feature 5: Landing gear

Common to all 737 generations is the main landing gear without a cover when retracted: when a 737 flies over you, you see the wheel hubs in the belly of the fuselage. That immediately distinguishes it from the A320 family.

Between the generations two details stand out. The MAX stands slightly higher at the front because the nose gear was lengthened – on parked aircraft the nose looks slightly raised. And the MAX 10 is the only variant with a special, telescoping main landing gear that extends on takeoff so that the long fuselage does not strike the ground during rotation. With the Originals you can also look out for a specialty: some 737-200s were fitted with a kit for unpaved runways, recognizable by a deflector on the nose gear. These aircraft flew, for example, in the Canadian Arctic, such as with First Air and Canadian North, or in Alaska. More in the guide Landing gear configurations as an identification feature.

Within the generation: determining the variant

Once the generation is settled, it comes down to length. Here it helps to read the proportions: how long is the fuselage ahead of the wing compared with the part behind it?

• Classic: The -500 is the short one, about 31 meters long and thus roughly as long as the old -200. The -300 measures around 33.4 meters, the -400 is around three meters longer and has a tail skid to protect against tail strikes.
• NG: The -600 is the shortest and carried no winglets from the factory. The -700 is the compact standard version, the -800 by far the most common NG. The -900 and -900ER are even longer; the -900ER has an additional pair of emergency exits behind the wing, which airlines can deactivate with low-density seating, however.
• MAX: The MAX 7 is just under two meters longer than the -700 and has two overwing exits per side instead of one. The MAX 8 corresponds to the -800. The 737-8-200 is a MAX 8 with an additional pair of doors behind the wing. The MAX 9 corresponds in length roughly to the -900ER, the MAX 10 is the longest 737 of all.

The additional door behind the wing on the MAX 9 is, by the way, a well-known topic: many operators have replaced it with a door plug, which is still recognizable from the outside as a door outline. Derived versions such as freighter conversions of the 737-800BCF or the 737-300SF/-400SF you recognize by the large cargo door on the left side of the fuselage and the missing windows. How to classify freighters in general is shown in Recognizing cargo aircraft.

Feature	Original	Classic	NG	MAX
Engine	JT8D, slim	CFM56-3, flat underside	CFM56-7, flat underside	LEAP-1B with chevrons
Winglets	none	rare, retrofitted	common (blended, Split Scimitar)	always (AT winglet)
Vertical stabilizer	low	with dorsal fin, low	clearly taller	same as NG
Tail end	blunt	blunt	blunt	long and pointed
Eyebrow windows	yes	yes	yes at first, later dropped	no
Production period	1967–1988	1984–2000	1997–2020 (passenger versions)	since 2016

Where you see which generation

In Germany, Austria and Switzerland you mainly encounter NG and MAX. Ryanair flies a pure 737 fleet of -800s and 737-8-200s, many of which you see, for example, at Frankfurt-Hahn Airport. TUIfly relies on -800s and MAX 8s, similar to SunExpress, Corendon Airlines, Smartwings or Norwegian. At Transavia you still mostly see the NG family. Their fleet composition changes constantly; who is currently using which variant is best checked in the respective airline profile and in current fleet lists (as of October 2026).

Classic aircraft in Europe today operate mainly as freighters, often at night. A 737-200 in passenger service you practically only see now when traveling to remote regions, such as northern Canada or Latin America. If you catch such an aircraft, it clearly counts among the highlights – how to put the rarity into perspective is explained in How rare is my sighting?.

Good places to see 737s side by side in peace are spots with a view of taxiways where the aircraft slowly pass by: for example the Affenfelsen in Hamburg or the Düsseldorf visitor terrace. There you have enough time to tick off engine, wingtip and tail one after another.

Typical mix-ups

• NG with Split Scimitar becomes a MAX: The most common mistake. Always check the nacelle trailing edge and the tail.
• NG without winglets becomes a Classic: A -700 or -800 without winglets looks older, but has the long NG wing and the taller vertical stabilizer.
• Classic with winglets becomes an NG: Rare, but they exist. Watch for the shorter wing and the lower vertical stabilizer.
• MAX 9 becomes a -900ER: Both have a similar length and an additional door behind the wing. Here again engine and tail decide.
• BBJ and military versions: Business-travel offshoots such as the Boeing Business Jets or the maritime patrol aircraft P-8 Poseidon are based on the NG and sometimes carry different wingtips. More on surveillance aircraft is in the guide AWACS, maritime patrol and reconnaissance aircraft.

When in doubt, the registration helps: through the registry you find out year of manufacture and exact variant. How that works is explained in Understanding aircraft registrations and How old is this aircraft?.

Conclusion

The 737 has looked familiar for almost six decades, yet every generation has its own signature. The engine sorts things roughly: slim tubes for the Originals, flattened nacelles for Classic and NG, serrated edge for the MAX. The tail confirms the MAX, wing and vertical stabilizer separate Classic from NG. You narrow down the variant at the end by length and doors. If you internalize this order, you need only a few seconds per aircraft at the fence. If you still mix up Boeing and Airbus in general, start with Telling Airbus and Boeing apart and the beginner guide Recognizing aircraft types.