17.3 Scuba-to-Flight, Alcohol/Drugs, and IMSAFE

ACS PA.I.H.K1g–l, K2, and K3 are fitness, scuba nitrogen, and the alcohol/drug rules. This is the chapter where a “I feel fine” story loses to a published number. The numbers that must be exact are AIM’s scuba waits and 91.17’s 8 hours and 0.04.

Scuba to flight — dissolved nitrogen, not “I only went to 30 feet”

At depth, pressure drives extra nitrogen into tissues. Climb into thinner air too soon and that nitrogen can come out of solution as bubbles: decompression sickness (DCS), the bends — classically joint pain, but also neurologic, skin, or respiratory trouble. PHAK: treat in-flight DCS as an emergency (oxygen, descend, land, specialist / hyperbaric care). Symptoms can even wait until after landing.

AIM 8-1-2(d) and the matching PHAK Chapter 17 figure are the PAR text. A pilot or passenger who will fly after scuba must give the body time to off-gas.

Three traps the written test writes on purpose:

1. 12 versus 24. Twelve hours is only the non-decompression dive, and only if you will stay at 8,000 feet or below. A decompression-stop dive is 24 hours even to 3,000 feet.
2. Actual flight altitude MSL, not cabin altitude. AIM says the 8,000-foot line is AMSL, not pressurized cabin altitude, because the cabin can fail. A pressurized climb to 11,000 MSL with a 7,000-foot cabin still uses the above 8,000 column: 24 hours after any dive.
3. Passengers count. The AIM sentence is “pilot or passenger.” Putting a just-surfaced diver in the back seat does not make the nitrogen legal.

Do not substitute a Navy table, a dive-computer “time to fly,” or a hangar “six hours if you feel OK.” PAR scores the AIM/PHAK waits.

91.17 — eight hours is not a feeling

14 CFR 91.17(a) says no person may act or attempt to act as a crewmember of a civil aircraft:

1. Within 8 hours after the consumption of any alcoholic beverage;
2. While under the influence of alcohol;
3. While using any drug that affects the person’s faculties in any way contrary to safety; or
4. While having an alcohol concentration of 0.04 or greater in blood or breath (grams per deciliter of blood, or grams per 210 liters of breath).

Those are independent. Clearing one does not clear the others. A pilot who had one beer six hours ago is already outside (a)(1), even if the BAC would be 0.00 and the pilot “feels fine.” A pilot who waited 8 hours but is still hung over or still at 0.04 fails (a)(2) or (a)(4). AIM 8-1-1 is blunter than the FAR: one ounce of liquor, one beer, or four ounces of wine can impair, remains detectable for at least 3 hours, and a hangover can impair many hours after the alcohol is gone. AIM’s “excellent rule” is 12 to 24 hours bottle to throttle depending on how much was drunk. That AIM advice does not rewrite 91.17; it explains why 8 hours is a floor, not a blessing.

91.17(b): except in an emergency, a pilot may not carry a person who appears intoxicated or under the influence of drugs (a medical patient under proper care is the exception). Your passenger’s bar tab is your 91.17 problem.

Drugs in (a)(3) include prescription and over-the-counter medication. AIM 8-1-1: tranquilizers, sedatives, strong pain relievers, cough suppressants, antihistamines, blood-pressure drugs, muscle relaxants, diarrhea medicine, and motion-sickness pills can all take judgment, memory, alertness, coordination, or vision. Anything that depresses the nervous system also lowers hypoxia tolerance. The AIM/PHAK safest rule: do not fly as a crewmember on any medication unless the FAA has approved that use. “The box said non-drowsy” is not an FAA authorization. Combo cold products are a classic 61.53 plus 91.17 stack.

91.17(c) and (d) add a testing duty: if law enforcement or the FAA has a basis to ask, a crewmember can be required to submit to, or to release, alcohol or drug tests taken within 4 hours after acting or attempting to act as a crewmember. That is how a “I waited 8 hours” story gets a number attached.

IMSAFE — official letters, official E

AIM 8-1-1 publishes the personal checklist the FAA wants memorized:

• I — Illness. Even a “minor” fever, infection, or allergy degrades memory, alertness, and calculation. Medication that “controls” the illness may be the larger problem. AIM: the safest rule is do not fly while ill; if you think that is too strict, call an AME, not a group chat.
• M — Medication. See 91.17(a)(3). New drug, new dose, or a drug you have not flown on is a no-go until an AME or the FAA says otherwise.
• S — Stress. Work, money, and family do not stay on the ramp. AIM: when difficulties are more than usual, delay the flight until they are resolved. Stress plus fatigue is called out as an especially bad pair.
• A — Alcohol. 91.17, plus hangover, plus the histotoxic altitude penalty.
• F — Fatigue. Acute fatigue is the ordinary tiredness after a long day, poor sleep, or heavy mental load; rest, sleep, exercise, and food fix it. Chronic fatigue is incomplete recovery between those hits; judgment goes, risk-taking goes up, and recovery needs a long rest (and sometimes a physician). Obstructive sleep apnea is an AIM 8-1-1 medical topic of its own.
• E — Emotion. AIM’s word is Emotion, not Eating. Anger, depression, anxiety, a fight, a death, a divorce, a lost job, or a financial crash can make a pilot unsafe. AIM: do not fly until you have recovered from an emotionally upsetting event.

Some instructors tack Eating onto the E as a nutrition reminder. Teach that as extra, not as the official letter. The card in AIM 8-1-1(i) ends in Emotion. Nutrition still matters; it just lives under PHAK’s dehydration/nutrition discussion and ACS PA.I.H.K1i, not as a rewritten acronym.

61.53 — the medical in the wallet is not a waiver

14 CFR 61.53(a) (operations that require a medical certificate): no person who holds a part 67 medical may act as PIC or as a required pilot flight crewmember while that person (1) knows or has reason to know of any medical condition that would make the person unable to meet the requirements for the medical necessary for that operation, or (2) is taking medication or other treatment that results in the person being unable to meet those requirements.

A third-class that expires next year does not authorize a flight with inner-ear congestion, a fever, a new narcotic, or a condition you have not told the AME about. 61.53(b) covers operations that do not require a medical (the 61.23(b) set): you still may not act as PIC or required crew if you know or have reason to know of a condition that would make you unable to operate safely. Sport-pilot / driver’s-license medical paths do not create a “fly sick” exception. BasicMed is a chapter 2 topic; 61.53 still asks whether you are safe today.

Dehydration, nutrition, hypothermia, fatigue, stress — K1g–j

PHAK treats these as aeromedical items, not lifestyle lectures.

Dehydration is a critical water loss. Heat, wind, altitude, and diuretics (coffee, tea, alcohol, many sodas) accelerate it. The first noticeable effect is often fatigue; then headache, cramps, sleepiness, dizziness. PHAK’s planning figure is two to four quarts of water every 24 hours, and to drink on a long flight whether or not you feel thirsty. Heatstroke is the next step: the body can no longer regulate temperature.

Nutrition is the other half of K1i. Skipping meals drops blood sugar and, PHAK notes, is especially ugly at night. Pack food. Do not substitute another energy drink for lunch and call it IMSAFE.

Hypothermia (K1j) is a drop in core temperature. A winter 172 with a weak heater, wet clothes, or a long descent in rain will take dexterity, speech, and judgment before the pilot admits to being cold. Stagnant hypoxia from cold-constricted circulation stacks on top. Warm, dry layers and a working cabin-heat system you have already leak-checked for CO are the mitigation — not toughing it out.

Fatigue and stress (K1g, K1h) close the loop. Acute fatigue hides until the first real error. Chronic fatigue looks like a personality change. Stress occupies the scan. Neither is cured by coffee in the run-up. If IMSAFE fails any letter, 61.53 is already in play.

Scenario: Priya, the reef, and the 6-hour beer

Priya finishes a morning non-decompression reef dive at 10:00. A friend offers a 17:00 sightseeing hop to 6,500 MSL. She had one beer at lunch at 11:00. She feels perfect. Two independent no-gos. AIM scuba: a non-decompression dive still needs at least 12 hours before a flight at or below 8,000 feet — 10:00 to 17:00 is 7 hours, not 12. 91.17: any alcoholic beverage starts an 8-hour clock, so 11:00 to 17:00 is 6 hours, which is already a (a)(1) violation even if her BAC is zero and she would pass a field sobriety test. If the same dive had required a decompression stop, the scuba wait would be 24 hours even to 6,500. If the hop were filed at 9,500 MSL, it would be 24 hours after any dive. Feeling fine is not a regulatory instrument.