Delta Air Lines Boeing 757 232 incident
Boeing 757 232 · Incident: uncontained engine failure during initial climb
From Atlanta, GA to Orlando, FL
Event
- NTSB case
- ENG18IA036
- Event typeAccident: someone killed or seriously injured, or the aircraft substantially damaged (NTSB definition). Incident: an occurrence that affected or could have affected safety, short of that. Glossary
- Incident
- InvestigationHow far the investigation had got when the record was published: preliminary, ongoing, final or completed. Unknown where the source does not say. Glossary
- Completed
- API-reported fatalities
- 0 · all aircraft and ground
- Ground fatalities
- Unknown
- OperationWhat kind of flying it was, grouped by the rules it flew under: airline (US Part 121), air taxi and commuter (Part 135), general aviation (Part 91 and similar), military or government. Glossary
- Airline
- WeatherVisual meteorological conditions (VMC): good enough to fly by looking outside. Instrument conditions (IMC): cloud or low visibility, flying by instruments. Glossary
- Unknown
Boeing 757 232
- Aircraft type
- Boeing 757
- Category
- Airplane
- RegistrationThe aircraft's tail number, such as N12345 or G-ABCD. Registrations are reissued, so the same one years apart can be a different aircraft. Glossary
- N668DN
- Operator
- Delta Air Lines
- Onboard fatalities
- Unknown
- Route
- From Atlanta, GATo Orlando, FL
- Aircraft age
- About 27 years (built 1991)
- Flight rulesThe regulations the flight operated under: in the US, Part 91 (general aviation), Part 121 (airlines), Part 135 (air taxi and commuter) and others; for flights abroad, the NTSB's coarser commercial or non-commercial code. Glossary
- Part 121: Air Carrier
- Phase of flightThe stage of the flight when things started to go wrong: standing, taxi, takeoff, initial climb, en route, maneuvering, approach or landing. Glossary
- Initial climb
- Defining eventThe single coded event the NTSB judges best describes what happened (records from 2008 on). Older records name the first occurrence in the sequence instead. Glossary
- Uncontained engine failure
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- Minor
Cause areas
No findings designated as a cause are recorded in the NTSB data yet.
Approximate · Coordinates from the NTSB case API, which marks them as estimated or does not say; no uncertainty radius is established.
NTSB narrative
The high-pressure turbine (HPT) uncontainment was caused by the failure of a rotating seal located between the HPT 1st-stage (S1) disk and 2nd-stage (S2) hub (the lenticular seal). The lenticular seal outer structure separated from an inner brace piece and unwound, destroying the turbine. Seal fragments breached the turbine cases. A fragment traveled forward, destroying the HPT S1 blades and penetrating the S1 turbine nozzle assembly and combustor, damaging a fuel nozzle stem, and releasing fuel.
The crack initiation site was destroyed by secondary damage. Although the failure mode was not determined, PW2000 engine lenticular seal cracks are a known failure associated with knife edge tip fatigue cracks that originate at the first or second knife edge tip and propagate down the knife edge pedestal to the barrel. Past root cause investigations determined that normal knife edge rub can cause local increases in knife edge tip temperature when the knife edge coating is worn and has begun to spall. Continued rub with degraded knife edge coating creates a heat affected zone at the knife edge tip that can lead to thermo-mechanical fatigue (TMF) and tip crack initiation. TMF is more likely to develop with second run seals matched with new honeycomb material.
Review of the engine service records found that the failed lenticular seal was installed new during a 2008 overhaul when the engine had accumulated 61,385 time since new (TSN) and 25,462 cycles since new (CSN). The seal was visually inspected and reinstalled during a 2013 overhaul at 74,042 TSN and 31,701 CSN. During the 2013 shop visit, 40% of the lenticular seal land honeycomb surface was replaced. The lenticular seal chromium carbide knife edge coating was not renewed, so that the second-run lenticular seal knife edges with chromium carbide coating ran against new honeycomb material. The lenticular seal failed 6,460 cycles after the 2013 shop visit.
An improved-design lenticular seal with the chromium carbide knife edge coating replaced with a more durable, temperature-resistant aluminum oxide coating was released by PW2000 SB 72-754 in 2011. The new-design seal was introduced as a part replacement on an attrition basis (use down-change part until exhausted).
Probable cause
A right engine turbine uncontainment resulting from failure of the high pressure turbine (HPT) lenticular seal due to a fatigue crack originating from an overheated region at a knife edge tip.
Contributing to the failure was Pratt & Whitney’s decision to introduce the temperature-resistant knife-edge coating as a new-part number lenticular seal on an attrition basis without the option to recoat existing lenticular seals, which delayed implementation of the more durable seal material into the fleet.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record ENG18IA036
- Event ID
- 20180913X21320
- Case number
- ENG18IA036
- Dataset
- full-current
- Source SHA-256
- 5cf380f0061817c0331a6b2d8cc7e0ee3a79bea469a1001dc5c10e56f35f5ab3
Source notes (4)
- Unreviewed is an editorial label, not an investigation status. API-sourced is not report-checked or human-reviewed. Explicit event totals are used without summing aircraft injury tables; onboard allocation is withheld. Unknown values remain unknown. The operation category is mapped from the NTSB-reported FAR part and has not been reviewed.
- Filled from the NTSB case API where the bulk record had no value: local date, investigation status, coordinates. Values present in the bulk record are kept.
- The date is the local date; the NTSB stores the UTC date 2018-09-06.
- API snapshot SHA-256: 0828657aea2d43ca2bed42208a31b60255745317e6855d15a3af3a1613f60c32; retrieved 2026-09-16T08:14:32.425Z.