Boeing 737.

Toward the end of the 1970s, Boeing realised that to keep pace with the market they had to update and modernise the Boeing 737.

At the Farnborough air show of 1980, initial specifications for what would become the Boeing 737 300 were released. This aircraft was larger with a seating capacity of 149 and a lengthening of the fuselage by 2.87 metres (9ft 5in) as well as an increase to the wingspan of 53cm (1ft 9in).

The original Pratt and Whitney JT8D-1 low bypass engines which sat under the wing protruding fore and aft were replaced by CFM56-3B-1 high bypass engines. Due to the low ground clearance of the aircraft the engines were hung on pylons from the wings to sit ahead of the wings. The air intakes were also not circular but rather flattened at the bottom to aid with ground clearance. Wing aerodynamics were improved as well as the offering of IFIS (Electronic Flight Instrumentation Systems) cockpits.

October of 1988 saw a further stretch to the Boeing 737 in the form of the Boeing 737 400, a variant that added an additional 3 metres (10 feet) to the fuselage length thus enabling a 170-seat capacity.

Alaska Airlines 737-900 with The Spirit of Disneyland II colours. Registration N318AS.

AeroMexico Boeing 737-800 registration N520AM landing at Miami FL(MIA) 17OCT2011.

Not all airline customers required the extra capacity offered by the newer versions of the Boeing 737. The Boeing 737 500 was launched in 1987 as a replacement for the Boeing 737 200. Being 48cm (1ft 7in) longer than the Boeing 737 200 and powered by the newer CFM56-3 high bypass engines the Boeing 737 500 showed a 25% fuel saving over the older variant.

The late eighties and early nineties saw serious competition offered by Airbus with their Airbus A320 model.  In 1991 Boeing began development on a new generation of aircraft. The Boeing 737 NG (Next Generation) group of aircraft includes the Boeing 737 600, Boeing 737 700, Boeing 737 800 and Boeing 737 900. This was the most significant update to the Boeing 737 so far, resulting in an all-new aircraft performance-wise, but still retaining important commonality with previous versions.

The wing was redesigned with greater chord and updated airfoil sections. The wingspan was increased by 4.9 metres (16 feet) giving a wing area increase of 25%. Coupled with the new CFM56-7B engines and increased fuel capacity, the range was increased by 900NM to 3,000NM. Winglets were also offered.

Modern avionics were offered as well as a modern cabin which was taken from the Boeing 777.

Boeing 737 MAX

As far back as 2005, Boeing initiated Project Yellowstone 1 (Y-1) to come up with an updated design building on the Boeing 737 Next Generation family. Incorporating technology from the Boeing 787 Dreamliner, the aim was to achieve fuel savings in the order of 20-25%. However, tests came back with results closer to 10%. It was found that you can't build a smaller Boeing 787 which is designed for different uses such as lower cycles(take-offs and landings) and carrying different systems for longer flights.

The project was shelved but not abandoned. New technologies had to be developed to enable the concept to become an actuality.

On 11 August 2011, the Boeing board approved the 737 Max development project. The new family of Boeing 737s would adopt the same variant numbering system as the 787, namely Boeing 737 Max 7, Boeing 737 Max 8, Boeing 737 Max 9, and Boeing 737 Max 10. The main driver, of course, was the need to come up with a newer more economical version of the iconic 737 city jet and remain competitive.

Airbus Industrie was well on the way to producing their new A320, the A320 NEO (New Engine Option) which would deliver a more economical version of the popular Airbus that is a direct competitor to the 737. After much research and analysis, it was determined that applying updates, improvements, and modifications to the current Boeing 737 model was by far the best option cost-wise and also speed-to-market-wise.

Boeing 737 MAX 8 in Boeing house colours.

The first Boeing 737 Max -8 fuselage completed assembly on 13 August 2015 at the Spirit AeroSystems plant in Wichita, Kansas.

This was a test aircraft and was eventually delivered to launch customer Southwest Airlines.  The completed aircraft, named "Spirit of Renton" rolled out of the Boeing Renton Factory on 08 December 2015. Nearly 49 years after the first Boeing 737 took to the air on 09 April 1967. The 737 MAX -8 took to the air on its first flight on 29 January 2016.

Boeing 737-9 MAX CFM LEAP-1B engine. The chevroned rear of the nacelle, like the Boeing 787, ensures a smooth laminar airflow over the engine casing. This is all part of the 737 MAXs fuel-saving economy.

Instrumental to delivering a more economical and powerful 737 is the CFM Leap 1B engine. This new generation engine uses the latest technology to deliver the cost savings that will take the 737 into the 21st Century. However, as has been the problem in the past with the low ground clearance 737, adding a larger engine has its own challenges. If you look at current 737s, like the 737-800 for example, you will notice that the engine nacelle is flattened at the bottom. This is to enable enough ground clearance. The Leap 1B is larger again. To enable it to be fitted to the 737 Max, the engine has been fitted to a pylon that holds the engine further forward from the wing and therefore can be set higher off the ground. 

In addition, the nose wheel strut has been extended by 8 inches to lift the engines higher.  The engines being further forward has caused a change to the aircraft dynamics in certain phases of flight. In those flight phases, it was found that the nose of the aircraft might pitch up, bringing about the possibility of a stall. To guard against this, Boeing installed a new system called the Manoeuvring Characteristics Argumentation System (MCAS). This system is designed to prevent the possibility of the aircraft entering a stall in the above-mentioned flight phases. The MCAS uses the horizontal stabilizer trim to push the nose of the aircraft down in cases where it senses a high angle of attack that may lead to a stall.

This view shows the distinctive Boeing 737 MAX winglet. Two smaller winglets mean that there is less weight required than for a more robust single longer span. In addition, it means that a significant amount of wing surface is added whilst still being able to fit into Gate size C at airport terminals.

Have we seen the last of the Boeing 737 Max problems?

The loss of two 737 Max aircraft with the tragic loss of hundreds of lives sent a clear signal to Boeing and regulators that all was not as well as it should be. The travelling public puts their utter faith in aircraft manufacturers as they strap themselves into their seats. When things go wrong, it destroys that faith, so not only do the problems need to be rectified, but they have to be done so in a very public and transparent way to restore that faith.

So what has Boeing been doing?

The problem as we recall is to do with the MCAS (Maneuvering Characteristics Augmentation System) which is a system that kicks in to stop the aircraft from getting into a stall situation in some very specific sets of unusual flight conditions. The need for MCAS was mainly brought about by the larger Leap 1B engines having to be placed on a longer pylon further forward of the wing to enable the required ground clearance below the engine when taxying. This created a slight change to the aircraft's aerodynamics which Boeing recognised and created a system to protect against a possible stall with a higher-than-usual angle of attack.

Boeing 737-347 Atlant-Soyuz Airlines registration VP-BBM

MCAS was designed to work in a situation where:

• The pilot is hand-flying the aircraft.

• The nose of the aircraft approaches a higher-than-normal angle of attack.

• The wing flaps are not deployed.

What Boeing has done is build more fail-safes into the system so that it doesn't activate until several cross-checks have taken place. The updated features are:

• Two Angel Of Attack sensors will have their data compared.

• Each sensor will send its data to the flight control computer.

• The computer will only activate MCAS if the data from both sensors agree.

• The MCAS will only be activated once so that pilots can then handle the situation instead of repeatedly having to fly against the MCAS.

• MCAS will never override the pilot's ability to fly the aircraft using the control column.

Boeing 737-33V EasyJet registration G-EZYO.

How does this differ from the original configuration?

The original MCAS based its activation on the data of a single Angle Of Attack sensor reporting on the attitude of the aircraft. In the case of Lion Air and Ethiopian Airlines, the single Angle Of Attack sensor fed back incorrect data to the MCAS. The data was repeatedly sent back which caused the MCAS to keep re-engaging on the receipt of each incorrect signal. This of course completely confused the pilots as they could see no reason for the Angle Of Attack readings nor the aircraft taking control of them each time it happened.

KLM Royal Dutch Airlines Boeing 737-900A registration PH-BXO.

You can see that both of those issues have now been addressed by Boeing. It is tragic, but often the way that lives have to be lost to move forward with technology.

As you can imagine, the Boeing 737 Max has now been scrutinised and rescrutinised to within an inch of its life. During that process, several other modifications have been mandated before an aircraft can go back into the air. Namely:

• Software updates to avoid a theoretically possible runaway stabiliser condition.

• Modify wiring in the horizontal stabiliser control system to be further apart to avoid the possibility of rubbing together.

• Checking all stored aircraft for FOD (Foreign Object Debris). Some instances of FOD were discovered in stored aircraft.

• Updates to software to avoid the remote possibility of autopilot disengagement.

The Boeing 737 Max is now in full production with orders looking healthy. If you have flown on a MAX be sure to let us know your thoughts below.

Air Europa Boeing 737-85P Registration EC-JBJ.

A Boeing 737 History Timeline.