{"as_of":"2026-11-06","attribution":"FAA and NTSB data via eFlight Registry (https://eflight.com)","connections":[{"group":"Applies to","items":[{"count":2428,"name":"Piper PA-24 Comanche","note":"","unit":"registered","url":"https://eflight.com/models/piper/pa-24#airworthiness"}],"relation":"applies to"},{"group":"System","items":[{"count":null,"name":"Other and general","note":"","unit":"","url":"https://eflight.com/systems/other"}],"relation":"about"},{"group":"More","items":[{"count":null,"name":"Every FAA order","note":"","unit":"","url":"https://eflight.com/directives"},{"count":null,"name":"Every aircraft system","note":"","unit":"","url":"https://eflight.com/systems"}],"relation":"see also"}],"graph":"https://eflight.com/graph","graph_index":"https://eflight.com/graph/index.json","license":"https://creativecommons.org/licenses/by/4.0/","node":{"effective":"1991-11-29","faa_document":"https://drs.faa.gov/browse/excelExternalWindow/A0194E08F84C594F862569A700559C7D.0001","id":"91-21-09","kind":"AD","name":"Airworthiness directive 91-21-09","published":"1991-10-28","subject":"Air Induction System","system":"other","type":"directive","url":"https://eflight.com/directives/91-21-09"},"source":"FAA Civil Aviation Registry, FAA airport file, NTSB accident database; assembled by eFlight Registry"}