For air taxis, a flap over birds

By Paul Brinkmann|April 17, 2024

Should air taxis be as resilient to bird strikes as helicopters of similar capacity? FAA says yes, but some disagree

Some developers of electric air taxis disagree with FAA’s decision to extend the bird strike rule for helicopters to the new breed of vertical takeoff and landing craft, although FAA shows no signs of bending.

The danger presented by collisions with birds has been notorious throughout the history of aviation. Most infamously, a flock of geese knocked out both engines on a US Airways A320 in 2009 shortly after takeoff from New York, prompting the emergency water landing dubbed Miracle on the Hudson.

Imagine what a bird or birds could do to an air taxi. FAA seems to have done so. The bird flap began in November 2022 when the agency published a draft airworthiness criteria document for Joby Aviation’s S4 aircraft, which also applies to similar aircraft in development by its competitors. These aircraft must be “capable of continued safe flight and landing after impact” on any part of the aircraft with a bird weighing 2.2 pounds (1 kilogram), or if the impact is on a propeller, with a bird of 4 pounds (1.8 kg), FAA said in the draft.

That’s enough to ensure that an average American crow won’t cause an emergency. Hitting a Canada goose, which can weigh up to 8 kg, could still be a serious problem.

Why the 1-kg and 1.8-kg specifications? FAA explained in the airworthiness document that the 1-kg specification comes from the existing rule for “transport category rotorcraft,” meaning helicopters, and that the 1.8-kg specification comes from the rule for certifying propeller designs against bird strikes. These bird weights have proven “to be sufficient,” it said.

When it finalized the Joby airworthiness criteria document on March 8, FAA noted that it received comments on the bird strike requirements from 20 agencies and companies, including the European Union Aviation Safety Agency, the General Aviation Manufacturers Association, Airbus and six other companies developing electric air taxis. FAA said these companies and groups asked it to “revise, remove, or clarify” the bird strike requirements.

Specifically, Airbus declared that “the requirements are not aligned with the EASA certification requirements” regarding the potential for multiple birds and the size of birds, and “this situation means validation of products will require additional demonstrations for both E.U. and U.S. applicants.”

Los Angeles air taxi developer Overair asked FAA to remove the bird strike rule, calling it “overly broad” because there are “no limitations on what speeds or altitudes must be considered, or on what structure.”

In the final document, the agency said it was sticking with the bird strike rule as proposed because of the “increased exposure to birds in the environment in which the S4 is expected to operate,” — below 4,000 feet — “the expectation of public safety, and the recommendations presented in the Aviation Rulemaking Advisory Committee (ARAC) Rotorcraft Bird Strike Working Group report” issued in 2019.

Daniel Schwarzbach was a member of that working group, and is a helicopter pilot and the executive director and CEO of the Airborne Public Safety Association, a Maryland-based nonprofit.

“Low level flight is riskier for bird strikes,” he says, adding that “With jetliners, bird strikes generally occur in the landing or takeoff phase. Certain areas are more at risk — for example, near a huge landfill where birds congregate — so you would avoid that.”

When Schwarzbach flew as an officer with the Houston Police Department, he had a turkey vulture smash through the windshield of his helicopter. Despite the mess and damage, he landed safely.

“It was at night, and me and my test pilot never saw the bird at all,” he says. “We recommend you wear the flight helmet, visor down, and bird strikes are the primary reason.”

For its part, Joby told me in response to emailed questions that it has been performing bird strike tests with its aircraft prototypes since 2017 on “structurally-critical aspects of our aircraft, including propeller blades.”

“For each area of the aircraft identified as structurally critical, we use analysis to determine the most critical point of the structure for an impact to take place and fire a surrogate bird at the structure. We then assess the damage to show no impact to continued safe flight and landing by demonstrating that the structure continues to meet strength requirements,” Joby said.

Beyond the airworthiness criteria, FAA continues to work toward publication of a general airworthiness standard for the powered-lift category that includes the S4 and refers to aircraft that take off and landing vertically and cruise on wings. In the meantime, powered-lift designs, including Joby’s, will head toward type certification “as a special class aircraft under existing regulations,” FAA wrote in its proposed rules for powered-lift aircraft.