A B-737 MAX 8 climbs through the clouds.

The narrowbody B-737, the best-selling jetliner in history, has been continuously manufactured since 1967. With more than 10,000 airframes built, Boeing currently has orders for more than 4,300 of the design’s fourth-generation model—the B-737 MAX, including those from Alaska, United, and WestJet.

Since the dawn of the jet age, ALPA has played an integral role in the development of new airframes. In nearly every phase of a new airframe’s design, production, and flight testing, ALPA members have been involved.

The development of the B-737 MAX 8 and 9 is no exception. As both F/O R.J. Eisemann (Delta) and I are ALPA Air Safety Organization Aircraft Design/Operations Group representatives and active B-737 pilots for our respective carriers, we spent several days with Boeing going over the finer points of the latest incarnation of the “Guppy.”

From many to one

The more than 367,000 individual parts that make up the B-737 MAX come from various locations and are assembled over 10 days at Boeing’s facility in Renton, Wash. Fuselages manufactured in Kansas, Mo., are shipped by train. At multiple points in their westward journey, they go through tunnels in the Rocky Mountains that afford only a three-inch gap on either side. Once in Renton, the fuselages are brought into a large hangar and moved through numerous stations where miles of electrical wiring are installed, wings are mated, and engines are mounted before the airplanes are flown to nearby Boeing Field for airline customization.

Engine design

Two CFM International LEAP-1B high-bypass turbofan engines power the aircraft. These new engines improve fuel efficiency by approximately 14 percent over today’s CFM-56 engines that power the B-737NG.

The engine-starting procedure for the B-737 MAX is the same as the procedure for the -737NG, except for a necessary slight increase in engine start times. However, when the LEAP engines start, there is a noticeably more rapid rise of the exhaust gas temperature rate as compared to the CFM-56 engines. In general and by design, the LEAP-1B runs faster and hotter than the CFM-56.

Due to reduced margins between the large turbofan and the engine cowl to maximize fuel efficiency, the rotors must be cooled sufficiently to allow them to shrink and straighten following the thermal expansion and “bowing” of the rotor after flight. After engine shutdown, it takes approximately 45 minutes for the rotor shaft to reach its maximum bow. Because 45 minutes is the typical turn time on the ground, the tight engine tolerances won’t allow for an engine to restart immediately without first cooling the rotor.

The electronic engine control automatically calculates the required “bowed rotor motoring” time, which can take between six and 90 seconds. It then displays a “motoring” icon on the N2 gauge while the shaft is cooling and straightening. When the icon disappears, a normal engine start can resume with fuel introduction above 25 percent N2, just as on the -737 NG. To protect the long-term efficiency of the LEAP-1B, the new recommended warm-up and cooldown time is three minutes.

To accommodate the eight-inch increase in diameter of the LEAP geared turbofan engines, the aircraft’s nose gear is also eight inches longer, which allows the aircraft to sit on a level horizontal geometric plane, making it more level than its predecessor. To maintain the equivalent sight on approach and landing and to accommodate the longer nose gear, Boeing takes advantage of the new fly-by-wire spoiler system installed on the airplane to employ the landing attitude modifier system, which is very similar to the system installed on the B-787.

The landing attitude modifier functions automatically at speeds 10+ knots above baseline Vref and is transparent to the pilot. The system works by slightly setting the flight spoilers in a “neutral float” position, thus increasing angle of attack and elevating the nose for landing to avoid premature nosewheel contact during flare and touchdown. The landing attitude modifier essentially ensures that the pitch picture for a higher approach and landing attitude will look similar to an approach flown at the baseline Vref approach speed.

A modern “front office”

In the cockpit, new LCD monitors have been integrated into the B-737 MAX, the same ones currently installed in the B-787 and the upcoming B-777-9. These larger displays have commonality with the B-737NG and can show all necessary instrumentation in the forward field of view.

Eisemann and I also had the opportunity to test several relatively new systems to the -737 family. While they were originally certified on the B-737NG as options, they’re available on the B-737 MAX as well.

The first system, which is basic to the B-737 MAX, is the roll command arrow, which aurally and visually tells the pilot the shortest direction to roll the airplane to a wings-level, stabilized flight in the event of an unusual attitude in the roll axis. The roll command arrow consists of a bold red-colored roll arrow that appears on the primary flight display (PFD) and heads-up display, if installed, during an unusual attitude. In addition, an aural warning of “roll right” or “roll left” aids the pilot in rolling the aircraft in the shortest distance to the horizon. The roll command arrow truly makes recovery from an upset condition simple and intuitive.

The expansive cockpit of the B-737 MAX features large LCD screens along with new safety features.

Next we were introduced to two new autopilot saturation alerts—“roll/yaw asymmetry” and “roll authority.” These alerts are intended to raise the pilot’s situational awareness that the autopilot is becoming “saturated” in its ability to maintain the desired lateral flight path due to any number of reasons (e.g., asymmetric flight controls, asymmetric wing icing, etc.).

During a simulated demonstration of a flap/slat asymmetry scenario, the first alert we observed was the roll/yaw asymmetry alert on the PFD, which indicated that the autopilot had reached 70 percent capacity of its total roll authority. As the condition further developed and the autopilot reached 100 percent of total roll authority, the autopilot became saturated, which caused the airplane to begin departing its intended flight path. The warning then upgraded to roll authority on the PFD and added an aural warning, notifying the pilot to take action and trim the airplane per the recommended primary rudder trim technique described in the Boeing Flight Crew Training Manual to return the airplane to its desired flight path.

It’s important to note that neither of these alerts indicate a new type of fault or failure on the -737. They simply increase pilot situational awareness for autopilot saturation events that may otherwise go unnoticed. These two alerts are optional on the B-737NG and basic on the MAX.

Lastly we experienced three new alerts designed to help prevent runway overruns due to unstabilized approaches that are continued to a landing, long landings, and/or ineffective use of deceleration devices upon landing. To trigger the first alert, we intentionally flew an unstable approach both high on approach path and fast on airspeed. This generated the in-air overrun warning, which both aurally and visually (on the PFD) directed us to go around, with the alert “overrun, go around.” The alert is generated when the system determines that given the airplane’s current energy state, entered runway braking action, and relative position to the end of the runway, there’s a high probability the airplane won’t be able to stop by the end of the runway if the approach is continued to a landing—even with the use of maximum brakes and reverse thrust.

We then conducted a normal landing, this time intentionally failing to use proper deceleration devices or braking. Shortly after touchdown, we received the new “speedbrake” warning, which indicated the speedbrakes weren’t deployed after landing. The speedbrakes, or ground spoilers, play an important role in getting the airplane to stop efficiently. As we continued down the runway, we finally reached a point where the system determined that the airplane would likely go off the end of the runway if maximum brakes and maximum reverse thrust (for the current condition) weren’t immediately applied. The PFD displayed “max reverse” in amber, and an aural alert “max brakes, max reverse” sounded. We immediately began maximum use of these deceleration devices and safely brought the airplane to a stop short of the runway end. These overrun alerts are optional on both the -737NG and the MAX.

Another noteworthy addition to the B-737 MAX is the elevator jam landing assist system, which deploys the fly-by-wire spoilers to a neutral position on approach when the system is activated by a new switch on the aft overhead panel. When activated, the system triggers a column force sensor. As the pilot pushes or pulls on the jammed control column to either increase or decrease the descent rate, the force sensor will either increase or decrease the amount of spoiler deployment from the neutral position to allow some amount of pitch control despite the jammed control column. There was a noticeable improvement in flying this scenario with the system activated.

Training and more

Pilots who are qualified on the B-737NG and will fly the B-737 MAX will receive computer-based training before flying the MAX on the same B-737 type rating. Boeing has demonstrated to the FAA that updates to the airplane are level “B” differences under FAA Advisory Circular 120-53B. Dozens of airlines around the world have successfully introduced the MAX into their existing B-737NG fleet using this computer-based training, which highlights the minor differences between the two airplanes.

The B-737 MAX represents the latest in technology, both on the ground and in the air.

For example, icing valves on all prior -737 models illuminate to a bright blue color to indicate valve transition and then switch to a dim blue to indicate that the system is in use. The failure of the icing valve to reach the commanded position is indicated to the pilot by remaining bright blue. With changes to regulations, all icing valve failures must now be displayed in amber. As a result, the wing and engine anti-ice lights on the MAX now latch on in amber if a failure occurs. There are approximately 13 new or changed lights or switches on the overhead panel of the B-737 MAX compared to the B-737NG as well as two deletions (ram door full open lights and APU EGT gauge).

Overall, Boeing has made smart and effective changes to the B-737 MAX to comply with aircraft certification requirements and/or requests by the FAA to update the airplane. For example, the B-737 MAX’s fly-by-wire spoilers now add a few more degrees of deflection in an emergency-descent scenario due to loss of cabin pressure to meet the most current regulatory descent compliance times.

Armed with our knowledge and experience, Eisemann and I spent several hours in the engineering cab, a fixed-based simulator that replicates the handling qualities of the B-737 MAX. We both agree that while there are noticeable differences between the B-737NG and B-737 MAX, the differences are minimal in day-to-day operations, and the airplane inherently flies the same as the -737NG. But as always, due diligence must be exercised when operating any aircraft to ensure compliance with fleet differences.