Sustainability Push Runs Up Against Safety

Airbus aircraft

As operators push to become more sustainable, safety professionals are increasingly eyeing the risks of unintended consequences.

Credit: Lutz Borck/Airbus

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Several years ago, a training captain and a new first officer were conducting a line training flight on an Airbus A320. Their departure clearance included an intersection takeoff, a takeoff roll that begins at a taxiway intersection instead of the runway end. It was also a rolling takeoff, meaning the aircraft could proceed as soon as it was lined up on the runway.

Company policy encouraged a fuel-saving single-engine taxi procedure, in which the second engine is started during taxi out.

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As the designated pilot flying, the first officer was responsible for taxiing the aircraft. The training captain’s pilot-monitoring duties included starting the second engine as the aircraft rolled toward the designated runway.

Soon after the captain confirmed the second engine was started and all appeared well on the instrument panel, he looked up and discovered the first officer had turned the wrong way at the intersection. Instead of accelerating down Runway 30 as assigned, the A320 was picking up speed heading the opposite way, down Runway 12. Fortunately, there was enough runway for the crew to get the A320 off the ground safely.

An investigation into the incident concluded the captain was preoccupied with preflight tasks, including starting the second engine. It also found that the operator’s single-engine taxi risk analysis and list of watch items for pilots focused only on the technical aspects of taxiing out on one engine, said Challenge Airlines IL Chief Operating Office Shai Gill, who shared the example at a recent Flight Safety Foundation (FSF) forum. No consideration was given to pilot workload or other human-factors ramifications, nor were pilots encouraged to weigh the benefits of potential fuel savings against the risk of adding complexity to the departure.

“That engine-out taxi period that was supposed to save a lot of fuel for the airline lasted slightly more than a minute during a 4-min. taxi time,” Gill said. “This is an example of how not to do sustainability safely.”

Sustainability is emerging as a key part of global airline strategies—both in the near term and well into the future. In the aircraft operations world, the push is forcing safety professionals to scrutinize the ramifications of sustainable practices and ensure they do not create unacceptable risk levels for an industry that has established an incomprehensibly high safety bar for itself.

The FSF in June based a two-day safety forum on the risks of sustainability. That event helped shape several sessions at the organization’s annual International Air Safety Summit in early November. More significantly, the observations shared at the June event prompted a working paper that delegates from the FSF and Singapore submitted to the International Civil Aviation Organization.

The paper flags four broad areas where potential threats are likely: carbon footprint reduction largely through fuel-savings initiatives; noise mitigation and air quality measures; the effects of climate change-related issues such as more severe weather; and pressures caused by nonaviation developments, such as biodiversity programs near airports that could create new wildlife hazards.

Taken together, these areas are influenced by many stakeholders, from government policymakers to customers who demand ways to offset their carbon footprints on flight segments. While operators are affected by all of them, they can control only a few. Focusing on these opportunities—most of them embedded in front-line operations—must become second nature for aircraft operators.

At its core, this means empowering pilots, Gill asserted. “A pilot’s job is to operate in the most efficient way possible while maintaining an acceptable level of safety,” he said. “A pilot has to be empowered to be able to decide what an acceptable level of safety is.”

Single-engine taxi procedures are one of several fuel-saving tactics where airline policy must leave room for a pilot’s judgment. Others include idle descents and policies that urge minimal use of flaps and reverse thrust.

Idle descents, in which an aircraft follows a steady, straight path from cruise to final approach instead of “stepping down” to different altitudes, save fuel and reduce noise. They also can lead to the aircraft becoming “stabilized,” or reaching the operator’s minimum requirements for key parameters such as final approach speed, position in relation to the runway and aircraft configuration, later than a step-down approach that gets the aircraft lower more quickly.

Mix in preferences to minimize flap usage and reverse thrust, and factors that contribute to runway overruns quickly begin to align, Gill said.

Such risks do not merit avoiding fuel-savings strategies. Rather, policies should be crafted to promote their use and emphasize the benefits, while also leaving room for pilots to evaluate the myriad factors that make each flight unique, Gill said. Instead of setting a broad compliance target of using certain procedures on 90% of all arrivals, for example, it might be best to establish an operations-wide target to save a minimum amount of fuel or lowering emissions by a specific amount. Then, track the numbers on an aggregate basis and show how they break down on a per-pilot or per-segment basis, while giving pilots the opportunity—but not a mandate—to review their individual performances.

Given the chance, many pilots might look at their individual numbers and compare them to the notional company averages. If the company has a well-established culture in place, many of those pilots might opt to contribute to big-picture goals, as long as it can be done safely.

“You have to empower your flight crew,” Gill said. “They can decide whether to reduce the safety margin on the spot—something that as an operator, you cannot do.”

Pilots also need proper training, he said, recalling the case of one airline that urged its pilots to use idle descents where possible, but always practiced step-down procedures during simulator sessions. Their rationale? There was no fuel to save in the simulator.

“You have to train like you fly,” Gill pointed out.

Sean Broderick

Senior Air Transport & Safety Editor Sean Broderick covers aviation safety, MRO, and the airline business from Aviation Week Network's Washington, D.C. office.


Delta must have broken the code; flew on dozens of DAL flights using single engine taxi.
In my opinion idle enroute descents are a sensible and safe way to conserve fuel. All that's needed to is for the pilot(s) to calculate the distance from the probable landing runway to start the descent. That's a simple calculation using VORTAC, TACAN, GPS, etc. Use the aircraft's glide ratio, adding or subtracting some mileage to adjust for a predominate tail or headwind. I would normally add 10 miles for final approach at a stabilized altitude, and possible maneuvering for unexpected traffic and runway changes. If during the descent it becomes necessary to reduce an established rate of descent, adding a bit of power easily solves that. If it turns out that some altitude needs to be lost more quickly, deploying spoilers / speed brakes easily solves that. As long as ARTCC cooperates, an idle enroute descent is the way to go when saving fuel is desired. It's completely safe.
Agreed that idle descents are a big (potential) fuel-saver, but a significant effort to coordinate with ARTCC will have to precede its widespread use.