The 737 MAX Engine Upgrade Issue
This is Part 3 of an in-depth investigative report by Aviation Reporter and Author of aviation books Thomas E. Gardner. In part 3 Mr. Gardner discusses how the 737 MAX engine upgrade became a significant issue in the development of the aircraft model. You can read Part 1 of the story HERE and Part 2 HERE.
This article of the multi-part series will examine the economic drivers involved in the 737 MAX engine/airframe upgrade process in more detail.
Review of The 737 Max Engine Upgrade Issue
As previously stated, Boeing, as well as its rivals, were constantly upgrading its currently popular airlines with newly developed cutting-edge turbofan engines.
Economic reasons cited were responsible for this accepted practice. This resulted in extending the usefulness of these existing airframes significantly regarding their range, fuel efficiency, payload capacity, and power.
This solidified each company’s bottom line while securing its profitability as well.
This is based on industry data made available around the time the major airlines and airframe manufacturers were considering the next series of upgrades to their aging fleet. This greatly influenced the decisions involved in the development of the Boeing 737 Max and Airbus A320 N.E.O. line of aircraft.
Improvements in turbofan engine design
It is apparent that the steady improvements in turbofan design and operation play a significant part in the total upgrade decision. However, these engine upgrades come with a price.
This improved efficiency is achieved largely in part to a steady increase in the bypass duct area, resulting in both a higher air mass flow rate around the engine core enlarging the engine inlet duct diameter.
This is the problem Boeing engineers had to deal with. Their answer to this dilemma would be tragically revealed in the 737 Max series of aircraft. This question remains:
Did Boeing sacrifice sound, prudent engineering practices in order to utilize these new series of turbofan engines?
The Re-engine Upgrade Cultural Overview
The re-engine upgrade process is more involved than it looks.
For example, the airline industry has found in the past that certain single isle short-haul airline models are easier to retrofit (upgrade) than actually purchasing an entirely new fleet of aircraft.
This practice of retrofitting over the years has evolved into a lucrative enterprise, especially for Pratt & Whitney, G.E., Rolls Royce and GFM [G.E. and Safron (formerly Semica) joint venture.]
However, in order to justify this course of action, the airline operations must weigh the total cost of ownership, which involves not only the purchase price of an aircraft but also the cost of operations (maintaining it), its depreciation and eventual disposal. This approach is usually effective when purchasing new aircraft rather than the current airframes in use.
Retrofitting existing aircraft
So, in order to justify retrofitting the existing fleet of aircraft, the airline companies in conjunction with the airframe manufacturers must consider three things. They are:
- Fuel burn reduction and future fuel price.
- Changes in engine reliability and maintenance costs.
- The impact on current fleet values.
Fuel burn improvements between the Boeing 737-200, 300 and 700 are noted in Figure 1.
A fuel burn reduction of 5.6% between 737-200, 300 and a significant drop of 9.5% regarding its 700 variant. This is a strong indication validating that these engine upgrades do provide a marked reduction in fuel consumption resulting in savings as well. The graph revealed in Figure 2 highlights fuel prices and its variability starting from 1991 through 2009.
However, this seemingly dated information reveals why the airlines and their airframe manufacturers like Boeing and Airbus felt justified with the constant power plant upgrade.
This natural progression led to the newest in high tech turbofans.
They would eventually become the GFM LEAPX (Leap1, Leading Edge Aircraft Propulsion) and Pratt & Whitney’s GFF (Geared Turbofan).
Changes in engine reliability and maintenance costs
Before the GFM Leap1 and Pratt & Whitney PW 1000 G geared turbofan engines became big news in the aviation world, its pre-decision involving the Pratt & Whitney JT8D, CFM56-3, and the CFM56-7 were popular and widely used power plants.
A significant amount of data has been compiled and used as a benchmark regarding the viability and profitability further validating this engine upgrade culture.
This information, however, is not at first easy to compile. This is often due to the cost comparison. Across the varying shops regarding the generations of fleet aircraft.
Age and its variation among the individual aircraft comprising the entire fleet make it hard to make a solid cost analysis. This involves airframe value/maintenance and its overall profitability in terms of the engine upgrade.
The FAA regulations mandate that the airlines submit detailed financial data to the Department of Transportation including maintenance costs.
737 variants versus A320 Engine maintenance cost
Figure 3 illustrates the engine maintenance costs in 2009 dollars/regarding the house of operation/fleet age.
According to the Figure 3 graph regarding the 737-300 fleet, retained an average life of five years and in 1992 averaging a $99/hour maintenance costs adjusted in 2009-dollar value. Likewise, the 737-700 fleet also averaging five years of age retained maintenance costs of $108/hour in 2007, measured in 2009-dollar value.
The graph in Figure 3 also reveals how these costs change as the fleet ages over time. This also involves the Airbus A320 fleet as well.
At this point in time, due to the overlapping time frames, a true and highly accurate accounting for all other airline fleets was not available. However, a decrease in maintenance costs regarding the 737-200 and 300 families can be clearly seen.
The entire concept of upgrading the existing airframes with new more powerful, efficient and quiet turbofans, depends on the money saved on the need for lower maintenance (increased on-wing life) and how labor-intensive the shop visit costs change when they are removed from the wing.
3 generations of 737s
The chart in Figure 4 highlights these improvements in scheduled maintenance regarding the three generations of 737’s and their respective turbo fan upgrades.
- The Pratt & Whitney JT8D offered on the 737 in 1968 required on average 6,000 flight hours between scheduled maintenance.
- The CFM 56-3 utili9zed in 1984 achieved 8,875 hours between maintenance intervals.
- The CFM 56-7 incorporated in 1998 achieved 17,750 hours.
Within 14 years the scheduled maintenance time interval doubled in terms of an increase in operational inflight hours.
Reduction in fuel consumption
Figure 5 expresses a uniformly positive per-flight-hour reduction in fuel consumption. This resulted in significant savings for both Boeing’s with their 737 family and Airbus with their A320 aircraft in use at that time.
Part 4 in the series will discuss the impact on the evolving turbofan technology and how it influences the engine upgrade culture.
Featured Image: Unsplash.
Story: ©2020 Thomas E. Gardner. Renowned Aviation Journalist & Author Thomas E. Gardner has spent months on his investigative report. The author has based his story on true facts that have been learned in regard to the 737 Max-8 engineering disaster during his in-depth investigation process of the article.
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