How to differentiate the various types of Boeing 737s

An Ethiopian Airlines Boeing 737 MAX crashed on Sunday, killing all 157 passengers and crew on board. The incident marked the second fatal crash in the short commercial history of the 737 MAX, following a Lion Air crash in October 2018. The two incidents had a lot in common. Both were brand new 737 MAX aircraft that crashed shortly after takeoff, when pilots failed to maintain a steady climb. In both cases, weather did not seem to be a contributing factor, suggesting that something else was responsible.

These two incidents have many passengers and crew asking whether the 737 MAX is safe to fly. A Miami-based flight attendant who wished to remain anonymous told TPG that she "no longer feels safe on the 737 MAX" and that she no longer "trusts" the aircraft. The Chinese and Indonesian governments have ordered their airlines to ground 737 MAXs, and Ethiopian Airlines, Royal Air Maroc and Cayman Airways have also suspended 737 MAX operations.

It's important to note that the 737 MAX represents a small subset of the overall 737 family. Since the first Boeing 737 was delivered to Lufthansa in 1967, Boeing has delivered more than 10,000 737 aircraft and has approximately 5,000 more orders on the books. Of these, only 350 (or 3.5% of all deliveries) are of the 737 MAX variant. Still, if you're trying to avoid traveling on a 737 MAX until an investigation into the Ethiopian crash is complete, here's how you can identify on which 737 variant you're flying.

A Whole New Generation of Aircraft

The 737 MAX aircraft are not the same as the older 737-700, 737-800 and 737-900 variants. While they share a name, 737s have evolved constantly and enormously from the machines that first flew in the 1960s. Today's 737s are very different airplanes from those made in the past.

The MAX variants use new CFM LEAP-1B engines, while previous generations of 737s use older CFM56 engines from the same manufacturer. The new LEAP engines help the MAX aircraft deliver huge fuel savings over the previous models, with a 10 to 12 percent increase in fuel efficiency. These improvements make the MAX cheaper for airlines to operate and allow it to fly farther. The smallest of the MAX family, the 737 MAX 7, can fly up to 4,400 miles, almost 20 percent more than earlier 737s. The MAXes also have other differences from the previous generation.

While we don't yet know the cause of the Ethiopian crash, and the Lion Air one is still being investigated as well, there's an important distinction from a safety perspective. Only the MAX models have the Maneuvering Characteristics Augmentation System (MCAS), software that automatically pitches down the nose of the plane to prevent a stall, which likely played a part in the Lion Air accident.

Telling Them Apart

The easiest way to identify a 737 MAX in person, as opposed to the 737-700s, -800s and -900s that make up the bulk of commercial fleets these days, is to look at the engines. The serrated "shark-fin" style engine casing is your first clue that you're looking at a 737 MAX.

Other versions of the 737 feature a perfectly round engine casing, like the 737-700 below.

If you see a 737 without the serrated engines, it's not a MAX. It could be any one of the previous 737s, models 300 through 900. The 300, 400, 500, and 600 are no longer in production.

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All MAXes also feature distinctive, huge "double" winglets at the end of the wing, and a tapered, elongated tail, as seen on this American Airlines MAX 8, while older 737s have shorter tails and different winglets. (Some don't have any winglets, but that's rare.)

737 MAXes are produced in four variants: MAX 7, MAX 8, MAX 9 amd MAX 10, in order of fuselage size and passengers carried. The 7 and 10 are not in service yet; the MAX 8 is the most commonly found, and the MAX 9 is flown in North America only by United Airlines.

Which Type of 737 Am I Booking?

While most passengers won't notice the difference between flying on a 737-700 and a 737-800, the airline and the FAA carefully catalogue which specific variant is used to operate each flight. As such, you can tell before you book which model of 737 is scheduled for your flight. Note that as airlines take delivery of even more 737 MAXs, and as some make the decision to ground their MAXs due to safety concerns, route assignments are likely to change and you should check back frequently or set an alert on ExpertFlyer for any aircraft swaps.

If you're booking a cash ticket, Google Flights should be the first stop for most searches. While Google Flights doesn't usually note the specific model of older 737s...

... It does clearly indicate when a 737 MAX is in use.

On flight-tracking sites such as FlightRadar24 or FlightAware, you'll see MAXes identified by four-digit alphanumeric codes. Each variant of the 737 MAX has its own:

• 737 MAX7: B37M
• 737 MAX8 / MAX200: B38M
• 737 MAX9: B39M
• 737 MAX10: B3JM

You can see below how this looks in practice, using FlightRadar24.com to study China Eastern Flight 5704, which flies from Beijing (PEK) to Kunming (KMG), and then on to Mangshi (LUM). The PEK-KMG leg had been operated until Sunday by a 737 MAX8 (B38M) while the KMG-LUM leg was operated by a 737-800, whose alphanumeric code is B738. Since China ordered the grounding of all 737 MAXs, the PEK-KMG leg is now scheduled with a B738 as well.

You can sometimes see three-digit codes referring to aicraft; in the case of the 737 MAX, there will always be an M in the code. On ExpertFlyer, searching under "Flight Details", you will see the MAX 8 referred to as 7M8:

One of the best features of ExpertFlyer is the ability to set alerts for upcoming flights. Normally I use this to let me know if award inventory opens up, but you can also set an aircraft change alert, which will automatically let you know if there's a change in the aircraft operating your flight.

Read TPG's full coverage of the Ethiopian Airlines 737 MAX crash and aftermath:

• More Airlines and Countries Join Growing List of Those to Ground 737 MAX
• How to Tell If You're Flying on a Boeing 737 MAX in North America
• Safety Experts Weigh in on the Boeing 737 MAX
• Boeing Cancels 777X Event Following Second 737 MAX Crash
• The Striking Similarities Between Lion Air and Ethiopian 737 MAX Crashes
• China Grounds 737 MAX Aircraft
• Ethiopian Airlines Boeing 737 MAX Crashes After Takeoff from Addis Ababa