ASN Wikibase Occurrence # 215167
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| Date: | Wednesday 5 September 2018 |
| Time: | 23:32 LT |
| Type: |  Boeing 757-232 |
| Owner/operator: | Delta Air Lines |
| Registration: | N668DN |
| MSN: | 25141/376 |
| Year of manufacture: | 1991 |
| Engine model: | Pratt & Whitney PW2037 |
| Fatalities: | Fatalities: 0 / Occupants: |
| Aircraft damage: | Minor |
| Category: | Serious incident |
| Location: | near Atlanta-William B. Hartsfield International Airport, GA (ATL) -
 United States of America
|
| Phase: | Initial climb |
| Nature: | Passenger - Scheduled |
| Departure airport: | Atlanta Hartsfield-Jackson International Airport, GA (ATL/KATL) |
| Orlando International Airport, FL (MCO/KMCO) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
Delta Air Lines flight DL1418, a Boeing B757-232, N668DN, experienced a right engine failure during climb after departing Atlanta-William B. Hartsfield International Airport, GA (ATL). The flight crew reported hearing a loud bang and noting airplane vibration and engine failure indications. The right engine was shut down and the flight returned to ATL where an uneventful single-engine landing was performed.
The airplane damage was minor. No injuries were reported.
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.
Accident investigation:
 |
|
Sources:
NTSB ENG18IA036
Location
Media:
The NTSB says it is investigating a reported uncontained engine failure experienced by #DL1418 on 5 Sept departing Atlanta. The aircraft, a 757 (N668DN) returned safely to Atlanta. https://t.co/0dB198Jpef pic.twitter.com/m4oD8fkYx9
— Flightradar24 (@flightradar24) 6 september 2018
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 06-Sep-2018 19:49 | harro | Added |
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