FAA Legal Opinion regarding §91.121 Altimeter Settings

Please read attached letter from the FAA and see IAC Government Committee Vice Chair Wayne Roberts comments below:

FAR §91.905 lists §91.121 Altimeter settings, as one of those FARs subject to waiver. And, we routinely advise waiver applicants to include this among their waiver requests. However, we recognize that not all waiver applicants may have done so, and that not all aerobatic fliers do so with benefit of a waiver.

In the absence of a waiver of §91.121, most FSDO inspectors would, consistent with FAA legal opinion, consider a pilot in technical violation were they found to have operated their aircraft with altimeter set to zero on the ground, as is typical (and, from my perspective, recommended) for practitioners of our sport.

Operationally, however, if an aerobatic pilot is flying under a waiver, the pilot should simply request waiver of §91.121 also. Waivers, even existing waivers, may be readily modified and amended. If an aerobatic pilot chooses not to fly under protection of a waiver, that pilot should be, legally, above 1500 AGL per §91.303(e). And, above 1500 AGL, it should make little difference to the aerobatic pilot that they had been required to set their altimeter to local barometer or field elevation, rather than setting it to zero on the ground.