Here is a question every city and airport planning an air taxi network should be able to answer: if a battery fire breaks out at a vertiport, who is responsible for putting it out?

Today, no one clearly is. FAA's airport certification rule, 14 CFR Part 139, "does not apply to… Heliports" (§139.1(c)(5)), and it is triggered only by larger passenger aircraft. Even at a certificated airport, a typical eVTOL seating plan does not drive the aircraft rescue and firefighting (ARFF) index the way airliners do. States are not filling the gap either: fire response is usually left to local coordination, and NFPA 418 (Heliports and Vertiports) still has no eVTOL agent quantities in its 2024 edition.

That is a design problem. The good news is that the design rulebook itself is finally moving.

One rulebook for vertical flight

On Oct 22, 2026, FAA posted Draft AC 150/5390-4, Vertical Flight Aircraft Infrastructure Design. It merges the heliport AC (150/5390-2D) and the vertiport engineering brief (EB 105A) and, once final, will cancel both. Congress required updated vertical-flight design standards in the 2024 FAA reauthorization (Pub. L. 118-63 §958).

FAA's industry letter and the AAM infrastructure page confirm the next steps: - Virtual Industry Day: Tuesday, Nov 10, 2026, 10:00 a.m. to 1:30 p.m. ET. - Written comments: due Jan 11, 2027, in FAA's Excel comment matrix only, to vertiports@faa.gov. - Final standards: FAA's stated target is summer 2027.

Until the AC is final, today's documents still apply. The draft is voluntary until final. Once final, AIP-funded projects follow current advisory circulars under Grant Assurance 34, and where Part 139 applies it is an acceptable means of compliance, so sponsors may want to read this draft as a design preview.

What's encouraging in the draft

The industry letter highlights performance-based organization (Standards vs. Recommended Practices), updated geometry based on landing-scatter research, a powered-lift "VTL" marking, on-airport aiming points as an alternative to a dedicated pad in some cases, and charger siting rules. That is real progress from EB 105A's interim posture.

It also shows where practice still outruns the book. Wisk's Oct 30 release on its Hollister Municipal pad said the site was "Built to existing FAA vertiport standards" and will feed eIPP data (Wisk). The accurate phrase today is "built to EB 105A guidance." The draft AC is not final, and Appendix H still sends sponsors to the ADO/FSDO for aircraft without a pilot on board. Sites are being built now; the comment period is how the book catches up.

Four questions sponsors should bring to Industry Day

1. Who fights the fire, and with what?

Problem. The draft defers fire protection to NFPA (and local adoption). Part 139 still misses heliports and small eVTOLs. Heliport foam tables were built for fuel fires; battery fires behave differently.

What to do now. Put a firefighting plan and mutual-aid agreement in every site package. Engage the NFPA 418 eVTOL work now, while it is still drafting. Ask FAA at Industry Day how AIP and state programs will treat battery-fire equipment at non-Part 139 sites.

Who pays, beyond FAA. AIP will not routinely buy ARFF vehicles for a non-Part 139 airport. State AAM funds, local public-safety budgets, and lease terms with operators are the near-term doors. Private capital still builds most pads; sponsors set the safety conditions.

2. Will the 15:1 approach actually be protected?

Problem. For powered-lift critical aircraft, the draft points to a 15:1 (or shallower) approach surface. Part 77 still protects 8:1 for heliports. Shallower surfaces are not evaluated by FAA the same way and are not charted for new objects.

What to do now. Protect the intended path through local zoning and the airport layout plan. Ask Industry Day how sponsors should document 15:1 protection before Part 77 catches up.

3. How do small and rural airports pay for readiness?

Problem. The AAM National Strategy says new vertiports will be "funded mostly by private sources." The NPIAS still has no vertiport category. Nonprimary AIP entitlements are small, and the temporary 95% federal share for many small airports drops back toward the statutory match after FY2026 unless Congress extends it.

As a former NASA contractor and the sole author of two NASA Contractor Reports, I reached the same conclusion in Assessing the Electrification of Aviation's Impact on the Airport and Airway Trust Fund and Regional Air Mobility: without extra levers, many small and rural airports will struggle to join electrified aviation. Fuel taxes most exposed to electrification were about 2.43% of Trust Fund revenue in FY2022, but locally that can mean roughly a 64% loss of avgas-equivalent gallons, fuel sales and related tax.

What to do now. Pair private and state money (Ohio's AAM action plan and Florida's AAM business plan are current examples) with early utility load studies. Ask FAA how the next AIP Handbook update will treat chargers, power and vertipads at nonprimary airports.

4. What happens to projects already in design?

Problem. When 2D and EB 105A are cancelled, projects mid-design need a transition rule.

What to do now. Ask for a grandfather paragraph for designs or grant/PFC applications approved or submitted before the effective date. Put that in the Jan 11 comment matrix.

The bottom line

FAA has opened the rulebook for building vertical-flight facilities. We still need clear answers on certifying, funding and protecting them, especially fire response and small-airport readiness. Industry Day is Nov 10. Comments are due Jan 11, 2027.

The best standards come from the people who have to use them. At a3i global aeronautics advisors, we help states, localities and airports plan and fund AAM infrastructure. Let's talk: a3iglobal.com.

This article is general information, not legal or tax/financial advice. AI tools assisted with research and drafting.