Airliners, family by family

Once you know the four checks on the identification page, the next step is telling variants apart within a family — which is mostly wingtips, nacelles, fuselage length and how many wheels are on each main gear leg.

Boeing 737 — four generations in one silhouette

Every 737 has the flat-bottomed nacelle, so the generation is the interesting question.

• Original (-100/-200) — long, slim, cigar-shaped nacelles slung close under the wing. Almost gone from passenger service.
• Classic (-300/-400/-500) — the flattened CFM56 nacelle appears here; no factory winglets, though many were retrofitted with blended ones.
• Next Generation (-600 to -900) — bigger wing, taller fin, blended winglets. Early builds still had the "eyebrow" windows above the windscreen.
• MAX (7/8/9/10) — split-tip winglets that point up and down, a larger LEAP nacelle with a serrated trailing edge, and on the MAX 10 a telescoping nose gear.

The rest of the Boeing line

• 757 — a narrowbody that looks stretched and over-engined, sitting high on long main gear. A pointed nose and a widebody-style flight deck. Most survivors are freighters now.
• 767 — the semi-widebody: one aisle short of a 777, 2-3-2 in the cabin, and the backbone of express air cargo as the 767-300F.
• 777 — very large twin with no winglets, raked tips on the -200LR/-300ER/F, and six wheels per main gear leg, which nothing else in service has. The 777-9 adds folding wingtips.
• 787 — raked tips with no winglet, chevron (sawtooth) nacelle trailing edges, and a wing that visibly flexes upward in the climb.
• 747 — four engines and the upper-deck hump. A short hump means an early -100/-200 or the stubby SP; the stretched hump is a -300, -400 or -8. The -400 has upright winglets, the 747-8 has raked tips and new nacelles. Freighters carry a hinged nose loading door, which is the easiest 747F tell of all.
• MD-80/MD-90/717 and DC-10/MD-11 — the leftovers of the T-tail era. Rear fuselage engines and a T-tail for the MD-80 family; a third engine buried in the fin for the DC-10 and MD-11, the MD-11 being the one with winglets.

Airbus

• A220 — formerly the Bombardier CSeries. Five abreast, a sharply pointed nose, and a geared turbofan whose fan is huge for the size of the aircraft.
• A320 family — round nacelle. Older aircraft have small wingtip fences or nothing; sharklets mark a late-build ceo or any neo. A318 through A321 differ in length and door count, and the A321XLR is the long-range one.
• A330 — same fuselage cross-section as the A340 with two engines. The ceo has a plain upright winglet, the neo a curved sharklet. Four wheels per main leg.
• A340 — an A330 with four engines, which is the whole identification. The -600 is extremely long for its wing.
• A350 — the dark "mask" painted around the flight-deck windows and a curved, upswept wingtip. The -1000 is longer, has an extra door pair and moves to six-wheel main bogies.
• A380 — a full-length double deck. There is nothing to confuse it with.

Regional jets and turboprops

Two rear-engined T-tails dominate, and cabin width separates them: an Embraer ERJ 135/140/145 seats three abreast (1+2) and is the narrowest airliner flying, while a CRJ seats four (2+2) — unsurprisingly, since it was stretched out of the Challenger business jet. The larger Embraer E-Jets (E170/175/190/195 and the E2 generation) moved the engines back under the wing and use a conventional tail, so they read as a small airliner rather than a big bizjet.

For the turboprops, look at where the main gear goes: an ATR 42/72 retracts it into a fuselage fairing, a Dash 8 / Q400 into the engine nacelles. Six-blade props mark an ATR -600 or a Q400; four blades mean an older Dash 8-100/-300.

Freighters

Dedicated freighters are often the most interesting thing on a quiet airfield, and they are usually the previous generation earning a second living: 767-300F and 777F on the express networks, 747-400F and -8F on the heavy and outsize routes, A330-200F, and converted 737-800s. A main-deck cargo door on the forward left fuselage, blanked cabin windows, or a nose door on a 747 all say freighter before you can read the titles.