Story ID: 
AINsight: Enhancing Sustainability Via Fuel and Oxygen
By: Jim Stabile
Caption: Higher diversion altitudes allowed by onboard oxygen use reduce aircraft fuel burn
Word Count: 659
The global aviation industry continues to place a high priority on sustainability—balancing economic, social, and environmental factors to ensure long-term health for both the planet and society. Significant strides have been made through technological advancements and behavioral shifts. Among the most effective strategies are aircraft weight reduction and optimized flight altitudes, both of which directly reduce fuel consumption.
One area receiving renewed attention is the interplay between fuel and oxygen systems, particularly in extended twin-engine operations (ETOPS) and overwater flight planning. This is especially relevant given the release of the revised SAE document AIR5648B, which explains the relationship between aircraft fuel and oxygen systems.
From PSI to Practical Metrics
Traditionally, aircraft oxygen systems were managed using pounds per square inch (PSI)—a measurement that offers little intuitive value to pilots during dynamic decision-making. AIR5648B moves the industry forward by introducing time- and distance-based metrics for oxygen management, aligning with the way pilots already manage fuel.
Time and distance are the currency of in-flight planning, and applying these to both fuel and oxygen reserves enables a more integrated and effective approach to emergency and contingency planning.
Under current rules, scenarios such as an engine failure followed by a cabin decompression require flight planning at 10,000 feet, where oxygen planning is not mandated. However, regulations do permit higher diversion altitudes provided adequate oxygen planning is in place. While these requirements are for flight planning purposes only, pilots retain emergency authority to deviate as necessary in real-time operations.
Flight planning to a higher equal time point (ETP) diversion altitude—for instance, 20,000 or 25,000 feet rather than the standard 10,000—can produce substantial fuel savings, often referred to in the airline world as “ETOPS ADD” or “ADD ETOPS fuel.” This is the additional fuel needed for lower-altitude diversions and is clearly marked in the fuel ladder on page one of most airline-type flight plans.
By planning to fly higher in an emergency diversion scenario, aircraft can reduce both the amount of contingency fuel required and the overall aircraft weight at takeoff, thereby increasing efficiency and sustainability.
Impact of Oxygen System Type
The extent of these savings depends on the type of oxygen system installed:
Gaseous oxygen systems—typically found on bizliners and some airliners—allow for extended high-altitude flight up to 25,000 feet. This makes them well-suited for higher-altitude ETP diversion planning and results in greater fuel savings.
Chemical oxygen generators (COGs) are limited to 12 to 22 minutes of supply. These are designed for emergency descent only and do not support prolonged high-altitude diversion. This limits the ability to plan for larger fuel-saving altitudes, but any increase above 10,000 feet will yield a savings.
In business aviation, where gaseous oxygen systems are common, operators can request a second ETP at a higher altitude using the same diversion airports. Flight-planning service providers can generate these comparisons upon request, and the pilot/operator can easily see the reduction in fuel required.
Fuel savings for ETP diversions can be significant. Business aircraft with three-hour ETP times can typically save 1,200 to 3,000 pounds of fuel. Widebody airliners have reported ADD ETOPS fuel values of 9 to 10 tons—fuel that need not be carried with higher-altitude planning, yielding both cost and emissions reductions.
A Strategic, Sustainable Shift
Oxygen is rarely used—only during decompression events—yet the weight of the system must always be carried. By leveraging technology and complying with existing regulations, pilots can now intelligently substitute oxygen capacity for excess fuel, significantly improving efficiency while maintaining safety.
In essence, fuel and oxygen are tradeable commodities in flight planning. With proper systems and tools in place, the aviation industry can unlock long-standing efficiency potential—one that aligns perfectly with its sustainability goals.
The opinions expressed in this column are those of the author and are not necessarily endorsed by AIN Media Group.