# How are jet engines certified against birdstrikes?

I recall that during US1549's birdstrike incident that resulted in it landing on the Hudson, a large amount of migrating geese weighing upto 20lbs each were sucked into the A320's engines — far bigger and heavier than previously certified.

I believe that at the time the engines were tested & certified by throwing small chickens or similar, one at a time, into the engines. Has this certification process been improved at all since this incident?

• youtube.com/watch?v=4nAc7wab-l4 – DeltaLima Apr 17 '14 at 23:51
• GE90-115B certification – DeltaLima Apr 18 '14 at 0:06
• Calvin and Hobbes teaches us that engineers drive progressively heavier trucks over bridges until they collapse to determine what the structural load limit is ("Weigh the last truck that made it and build an identical bridge"). Why shouldn't bird strike certification be the same: Throw progressively larger birds at the engine until it blows up (or you've shredded an Emu)! – voretaq7 Apr 18 '14 at 5:16
• I believe they actually use mammals, starting with naked mole rats and working up to baby elephants. The higher bone-density means that if an engine can withstand a human (or equal) sized mammal, then a bird of that size will be even less stressful. – Keegan Aug 14 '14 at 18:22
• The bird strike occurred on January 8th. Which way were the geese migrating? – DJohnM Jul 7 '15 at 0:10

There are hundreds of tests that need to be performed for certification of a turbine engine.

The FAA requirements and tests are listed in CFR part 33 E and F.

Amongst them are:

• Maximum static thrust tests
• Vibration tests
• Endurance tests
• Water ingestion test
• Hail ingestion test
• Ice cloud test
• Bird strike test

A number of them can be seen in this video of the GE90-115 Engine

The specific requirement for bird ingestion are described in §33.76. The number of birds to be used and their weight depends on the area of the engine inlet.

There have been several changes to the bird ingestion requirements for certification since the A320 engine was certified in 1996. However, once an engine is certified there is no need to demonstrate compliance to the updated requirements; the engine remains certified as it was.

The latest update to these requirements was in 2007, prior to the Hudson accident. To answer your question: no, there have not been any changes to the bird strike testing requirements of engines in the aftermath of the Hudson accident.

• Actually, reading the NTSB report, changes were made regarding bird ingestion certification, after the certification of those engines. Also, the NTSB recommends ... the FAA specifically reevaluate the 14 CFR 33.76(d) large flocking bird certification test standards – Danny Beckett Apr 18 '14 at 0:33
• @DannyBeckett That is a recommendation. Recommendations take time to be followed up, if they are followed up at all. Changing certification test standards is not done overnight. It is a long process of debating and reviewing requirements with a committee of experts from industry and government. – DeltaLima Apr 18 '14 at 6:45
• Sure, but the report specifically mentioned in verbose detail, that the certification requirements had already been changed. – Danny Beckett Apr 18 '14 at 6:46
• @DannyBeckett but if you look up 33.76, you see that the latest amendment was in 2007, prior to the accident. – DeltaLima Apr 18 '14 at 6:48
• @DannyBeckett probably true. Once something is certified it needs not to be recertified if the certification requirements change afterwards – DeltaLima Apr 18 '14 at 7:08

There are multiple various requirements, for instance:

• After "swallowing" a smallish goose (formally up to 3.65kg) the engine must still pull at least half of the thrust for at least 14 minutes, and must not become dangerous for the plane (no fire, no uncontained failure).
• After ingesting a flock of ducks (16 birds no more than 0.85kg each) the engine must still work for about 20 minutes.

There are also requirements for various sizes and number of birds in between, and some requirements depend on the inlet size. In general, seems that after the bird strike the engine is required to stay safe and even work for some time, but not for long.