Boeing 737 NG and 737 MAX Differences

The 737 NG (Next Generation) and the 737 MAX are the third and fourth generations of the Boeing 737. They are related aircraft on one FAA type certificate and share the FAA pilot type rating B-737, so a pilot moves from one to the other through differences training rather than a new type rating course. The 737-8 has the 737-800's length and, apart from a few items, its normal procedures, but it has new engines, new wingtips and tail cone, a new display system and a set of system changes, several of them revised after the 2019 to 2020 grounding.

The differences, and the training each one needs, are recorded by the FAA Flight Standardization Board (FSB) in its 737 report, here Revision 17 of November 2020 and the Revision 21 draft, and by EASA in its type certificate data sheet (TCDS) IM.A.120, Issue 29. Systems are described in detail in the other B737 articles; this one compares the 737-800 and the 737-8, the pair the FSB evaluates. For the principles see FSB reports and differences training.

The 737 generations

EASA's return to service report traces four generations, and the FSB names them as four series groups on FAA TCDS A16WE:

The NG brought a larger wing as well as the CFM56-7; the 737-800 was certified on 13 March 1998. Boeing launched the MAX in August 2011 around the larger, more fuel-efficient LEAP-1B and applied to amend the existing type certificate for a derivative of the 737-800, the 737-8. The 737-9 was certified in February 2018 and the 737-8200, which the FSB found functionally equivalent to the 737-8 in January 2021, in March 2021. The 737-10 is not in the FSB tables or the EASA data sheet used here.

A type certificate data sheet is the authority's summary of a certified type: models, certification basis, engines, dimensions, weights and limits (type certificate data sheets). EASA's lists each model's FAA certification date and EASA validation date, the 737-8's being 27 March 2017.

LEAP-1B engines and nacelles

The LEAP-1B is larger and more powerful than the NG's CFM56-7B, and because of its size it is mounted higher and farther forward. Two consequences follow. The nose landing gear is 8 in longer, to give the larger engine ground clearance. And in small parts of the flight envelope, approaching the stall and in higher-g maneuvering, the new engines would make the control column feel lighter than the regulations allow, which is why the MAX has MCAS (see below).

EASA classed the new powerplant installation as a significant change. The TCDS lists the LEAP-1B25, -1B27, -1B28, -1B28B1 and -1B28BBJ1, and 19.25 L of usable oil against 10.3 L on the NG. The FSB grades the engines Level B with a procedure change and lists the changes that come with them:

• the electronic engine control loses the NG's overboost rating and gains an icing idle speed;
• the engine display has a revised format and no compact format;
• a THRUST alert and a MOTORING indication for bowed rotor logic are added;
• the NG's REVERSER light becomes REVERSER LIMITED, and REVERSER COMMAND and REVERSER AIR/GND alerts are added.

On the NG, hard alternate mode can give an overboost with the thrust levers at the forward stop, so a converting pilot checks what the forward stop gives in the MAX FCOM rather than carrying over the NG wording (B737 engines and engine indications).

Aerodynamic changes: winglets and tail cone

The Advanced Technology winglet takes the place of the NG's wingtip, which is either plain or fitted with a blended or split scimitar winglet. Announcing it in May 2012, Boeing said its aerodynamicists had used computational fluid dynamics to combine raked-tip technology with a dual-feather winglet concept, balancing the gain in effective span between the winglet's upper and lower parts, and that the design fits within existing airport gate constraints while its extra effective span reduces drag. In the TCDS the 737-8 spans 35.92 m (117 ft 10 in) with winglets against the 737-800's 35.79 m (117 ft 5 in), stands 12.29 m high against 12.57 m, and has the same 39.5 m (129 ft 6 in) length.

The FSB groups the blended, split scimitar and Advanced Technology winglets in one item. Operators flying 737s with and without winglets train the differences at Level A: the dimensional changes, with emphasis on the lower strake's ground clearance, the takeoff and landing crosswind guidelines, and the ground contact angles in a normal landing. The underlying aerodynamics are in induced drag and wingtip vortices.

At the tail, Boeing's design decisions of April 2012 extended the tail cone and thickened the section above the elevator to steady the airflow, which removed the need for vortex generators on the tail; Boeing said the changes would reduce drag. Its firm concept announcement of November 2012 listed the redesigned tail cone, with the LEAP-1B engines and the Advanced Technology winglets, among the MAX's fuel-saving changes. The MAX also carries two tail anti-collision and position lights where the NG has one (Level A).

Large displays and the flight deck

The NG's Common Display System has six display units. The MAX replaces them with a large display system of four liquid crystal displays from Rockwell Collins, which the FSB calls the MAX Display System (MDS) and grades B/B. Boeing kept the look and feel of the NG display formats to preserve training commonality across the family, so much of the change is in where things appear and which switch moves them.

The FSB lists no change to the mode control panel. The two-position gear lever is the change most felt in practice: NG procedures move the lever to OFF after retraction, and the MAX has no OFF, so the after takeoff checklist changes and gear handle operation is an FSB special emphasis item. Display details are in B737 flight instruments and displays.

System differences

From the 737-800 to the 737-8, every item in the FSB design differences table is Level A or B. The FAA describes the MAX crew alerting system as based on the NG's, with select alerts changed or added.

EASA records that the spoilers became fly-by-wire to reduce weight and build time. MCAS lives in the flight control computers as part of the speed trim system. The FAA explains that the MAX was designed to handle and feel the same as the NG, and that MCAS adds nose-down stabilizer trim at elevated angle of attack, only in manual flight with the flaps up, to give the column force the rules require. Its original design relied on one angle of attack sensor at a time; the update that returned the MAX to service compares both, allows one command per high angle of attack event and limits the total so that the column alone can always control pitch. The details are in B737 flight controls: pitch and stabilizer trim and 737 MAX return to service.

Differences training levels

The FSB grades every difference between related aircraft by differences levels, written training/checking:

The master differences requirements table, the minimum for the whole move, reads (E*) B/B from the 737NG to the 737 MAX in Revision 17 and E*/B in the Revision 21 draft, B/B back to the NG and A/A between MAX models. The E* points to Appendix 7, the special training every pilot must complete before operating the MAX: ground training, through Boeing's MAX CBT or an approved equivalent, on seven non-normal checklists, MCAS, the autopilot flight director changes, manual trim and unreliable airspeed, and five events in a Level C or D simulator. Three need a MAX simulator (MCAS activation, the cross-FCC trim monitor and an erroneous high angle of attack on takeoff); the two manual trim exercises may be flown in an NG simulator.

No supervised line flying is required between the NG and the MAX in either direction. Revision 17 adds no currency rule; the Revision 21 draft accepts Level B differences training for currency between the two once the initial E* training is done. For mixed fleet flying the FSB recommends alternating the proficiency check between series groups, every 6 months for captains and annually for other pilots. Autoland is identical on both and needs no differences training unless the pilot changes between fail passive and fail operational systems.

In Europe the MAX's flight crew data, Boeing document D626A014, are required for entry into service by an EU operator; it is the same document number as the NG's, whose type rating the TCDS gives as "B737-300-900". EASA's return to service added five training areas of special emphasis: stabilizer trim, runaway stabilizer, flight control computer and MCAS functions, unreliable airspeed, and multiple alerts in non-normal conditions.

Operational differences for crews

For a crew moving from the NG, the differences felt in daily operation are mostly these:

• Walkaround: the longer nose gear, two tail lights and, on some 737-8s and every 737-9, a two-position tailskid.
• After takeoff: no gear lever OFF position.
• Trim alerts: on the MAX, SPEED TRIM FAIL staying lit after the master caution reset means MCAS and speed trim are lost for the flight; STAB OUT OF TRIM lit on the ground below 30 kt means the cross-FCC trim monitor tripped in flight, and takeoff is not permitted.
• Angle of attack: AOA DISAGREE, shown when the vanes differ by more than 10° for more than 10 seconds, is standard and leads to the airspeed unreliable checklist.
• Stick shaker: in pitch modes without speed protection, except flare and dual-channel operation, the autopilot disconnects one second after stick shaker onset and the flight director bars clear.
• Dispatch: the revised FAA master minimum equipment list requires both flight control computers for passenger dispatch.
• Weights and limits: the TCDS maximum takeoff weight is 82,645 kg for the 737-8 against 79,015 kg for the 737-800, and both have a 41,000 ft maximum operating altitude. A 15 kt tailwind is listed for the MAX as demonstrated capability, not an approval above 10 kt.

At the January 2021 return to service EASA also prohibited RNP AR operations in its MAX flight manual. As always, the operator's AFM, FCOM and QRH govern.

Library articles are written for study and exam preparation. They do not replace your aircraft's approved documentation, your operator's procedures or the regulations themselves.