Chesley’s “burned bird” Account Smells Funny

“[…] I smelled what I described at the time, and I still would, as a burned bird smell brought from the engine air into the conditioning system of the airplane.” (Chesley Sullenberger on CBS “60 Minutes” http://www.youtube.com/watch?v=u1LmBHEmr9U)

In order for a pungent odor from a jet engine to fill a cabin there has to be a substantial and steady odorous supply of pungent molecules emanating from the engine. But a bird, even a big goose, passes just too fast through an engine to achieve this. The destructive damage inflicted on the engine from a bird ingestion can certainly result in foul cabin air, but so can a compressor surge which came a whisker from blowing up the right CFM-56-5B4/P engine on Cactus 1549 two days earlier over Newark. A collision with an entire flock of large geese must also produce a series of rapid distinguishable loud thumps, like sandbags. Only one bang was heard on Cactus 1549 and it came from, not the right, but the left engine with no other accompanying sounds.

The air piped aboard modern airliners is second in purity to a modern hospital operating room. Air is supplied by an Environmental Control System (ECS), literally a life support system. The ECS sterilizes and re-circulates cabin air, pressurizes the airframe, replaces all onboard air 3-4 times/hour, regulates cabin temperature, helps power pneumatic systems, supplies the heat for wing de-ice and potable water, keeping all onboard alive in a humanly unsurvivable environment that without everyone aboard would perish.

Occasionally, you’ll hear or read (most likely on an internet forum site) airline transport pilots swear that they smelled the “KFC smell” after a bird ingestion. The trouble with this is that wild birds that fly into jet engines aren’t gussied up in 11 of the Colonel’s secret herbs and spices and deep fried in grease and/or cooking oil to smell a block away. Wild birds aren’t seasoned by a spice rack and there’s no cooking grease/oil in the core for deep frying. We can take such claims with a huge grain of salt.

To offer a time frame perspective on the impossibility of Sullenberger’s bird smell claim, Cactus 1549 was traveling 175kt at the purported bird strike point. At this speed the 8.5’ long CFM 56-5B turbofans were traveling their length in 35 milliseconds or ten times faster than the blink of an eye. At 90%+ N1 on departure power setting both engines would suck any wayward goose through the fan disk and accelerate its shredded legacy through the engine core or bypass at even fewer milliseconds since producing thousands of pounds of forward thrust to propel and climb the A320 that can weight up to 206,000lb on takeoff. Each engine pushes up to 103,000lb through the air in a positive climb, resulting in a massive volume per minute rushing though each engine and much more in 35 or less millisecond time frame than a large goose's volume. A goose would pass through and exit the 8.5’ length in thousands of shredded pieces faster than ten times faster than a blink of an eye and the only time interval that any ‘burned’ goose particulates would be available to contaminate the onboard air supply. For contrast, the leader bolt from a lightning strike strikes in about 20 milliseconds. An ingested bird would, therefore, approach ‘lightning’ velocity through the core and out the exhaust.


The ECS draws air from engine ‘core’ bleed air ports located at the low and high pressure turbine stage and variable geometry ram air inlets on the fuselage bottom between the wings.

The bleed port diameters are mere inches across and to draw in bird particles these would have to pass right over the selected port or ports in use aperture(s).

Chesley Sullenberger’s above statement infers that there’s a direct air supply from the bleed ports to the cockpit and second, at near lightning strike velocity a sufficient concentration of burned goose particles passed over an open port(s) and wended their way to the cockpit unimpeded, up his nostrils, which he then detected and identified as “burned bird” and, coincidentally, only person onboard to do so. Fuggedaboudit!

At takeoff and initial climb the low pressure turbine stage air temperature is 400* F, but its pressure is only 30-40psi, too weak to handle all the needs of the aircraft. So the high port at 1200* F and 430psi handles all the ECS duties until the aircraft achieves sufficient forward speed for the ram inlets to provide adequate air flow. While parked at the gate there is zero functional air flow through the ram air inlets due to zero knot forward speed, so only the bleed ports can draw in air.

The trouble is Jet A-1 auto-ignites at 410 *F, so to avert any fire from a possible fuel leak the high port air temperature is reduced to below 410 *F by a heat exchanger called a precooler. The very first stop for the high port air in the ECS process after entering the aperture at 1200 *F, a temperature that easily sterilizes any living microorganism, is an exhaust that dumps most of the 1200 *F air overboard, my guess is two-thirds, to shed over 800 *F from the remaining air that then travels into the pneumatic manifold. The majority of Chesley’s “burned bird” particles drawn into the high port would be sterilized and then tossed overboard before entering the manifold.

The now sub auto-ignite and still highly pressurized air eventually passes through a centrifuge and coalescer bag that separates water molecules and any heavier than air particle, including goose, and dumps these overboard too.

What are the chances of the high port drawing in goose particles versus the other thousands of cubic feet per second of ‘clean’ air? And how much air can the high port draw in 1/35th of a second?

The Airbus ECS supplies at least 20 cubic feet of air per minute per seat (passenger, attendant and crew) onboard, whether occupied or vacant. 10cf originates from the bleed ports and rams (though just bleed ports on taxi, takeoff and initial climb) added to an existing 10cf/seat of sterilized and recycled cabin air. The recycled cabin air is multiple HEPA-filtered to 99.99% particulate-free and so filter sterilized, and the other half (at takeoff and initial climb) is compression heated sterilized high port air blended with HEPA-filtered cabin air in an air mix manifold, all water-separated and coalesced, which makes the recycled cabin air doubly sterilized and why second in purity to operating rooms. At takeoff the high port handles all the ECS duties of supplying the 10cfm requirement of new air per seat, say 185 seats total, but since two-thirds is dumped overboard by the precooler the high port will draw in an initial 30cfm/seat for a total of 5550cfm (figures not accurate but reasonably close) before two-thirds is soon dumped. This breaks down to 2.6cfm of maximum possible draw of goose particle contaminate air volume of undetermined “bird smell” concentration in the <35 millisecond bird ingestion interval. Therefore, only 0.87cf will survive the precooler dump, already sterilized, then water- and particle-separated, before pumped in even distribution up and down the entire cabin and blended with at least 5550cf of existing uncontaminated air pumped out of the cabin vents at about 500ft/min and deliberately directed away from the face and hands. Sullenberger, and only he, got a whiff of bird, did he?

To smell any odorous contaminant in the cockpit via the bleed air ports the source must originate in the engine core and at a molecular concentration high enough for the human olfactory system to detect would require being apropos to downwind of a barbequed goose or something to this effect. But a 4” long Canada Geese feather was supposedly found in the left engine outer bypass, which it couldn’t have as explained in another article, totally isolated from the core by a hermetically isolated metal boundary and nowhere near the bleed air port aperture for goose particulates to be drawn in, then somehow survive the precooler dump, then centrifuged and again dumped, mixed with 99.99% particulate-free cabin air and then pumped up Sullenberger’s nose and no other’s. Although it is possible for goose material from the same bird to pass through both the core and bypass, the core material would be shredded, pulverized and heat sterilized from the 430psi in the high compressor stage.

What do sterilized goose particles smell like? Probably not much, they've been crushed by 430psi and heated to 1200*F. Every microorganism has been destroyed. Most of the food we eat, including bird, is sterilized. Its taste is not natural, but from synthetic chemical additives simulating the real thing and accurate enough to fool the human olfactory system. Unless the A320 has a cockpit-mounted synthetic bird chemical additive dispenser, Sullenberger would never smell burned bird. To smell burned bird, the bird first has to burn. If you flick your finger through a propane torch flame, will it be burned? Nope. Do bird particles, moving >175kt, have time to burn at 1200*F under 430psi before dumped overboard at the precooler? After many minutes subject to this heat it will, but not in 35 milliseconds even at 1200 *F. What will emit a powerful pungent odour from internal engine destruction are leaking engine seals whose escaping contents 'smoke' under the intense heat and pressure due to a continuous long-lasting supply as directly opposed to a <35 millisecond dosage.

All of the above concerns a functioning turbofan system. The left engine, however, shutdown. Once the shutdown occurred, and after any ingested bird would exit the engine unit, the high port turbine would shutdown, drastically dropping the temperature and pressure, knocking out the water-separating centrifuge and recirculation fans. How do molecules of “burned bird,” sterilized by 430psi to 1200 *F, which incredibly beat out every other cubic foot of clean air in the core to enter the high port, survive the precooler dump and water-separator, wend their way from near mid-left wing to the cockpit by quickly waning turbine power from a miniscule window of opportunity, then overwhelm the powerful stench of smoking engine lubricants and oil in only 0.87cf to pull it off?

I’d say Chesley might want to spice up his statements that he gave to the House Transportation and Infrastructure Committee hearing (in theory) on US Airways Flight 1549.