Cessna 501 N75TL

Summary

On 31 December 2020 at about 22:15 local time, a Cessna 501 registered N75TL, operated by Interstellar Air LLC, was involved in an incident near Opa Locka, Florida, United States. One person was on board and nobody was injured. The aircraft was slightly damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

31 December 2020 at 22:15

Classification

Incident

Location

Opa Locka, Florida, United States

Nearest airport

Opa Locka Executive Airport (OPF)

Coordinates

25.9070, -80.2780

Aircraft

Cessna 501

Registration

N75TL

Category

Airplane

Engines

2

Operator

Interstellar Air LLC

Operating rule

Part 91: General Aviation

Purpose of flight

Personal

Phase of flight

Not recorded

Route

Opa Locka → Willston

Aircraft damage

Minor

Weather

VMC

Light

Day

NTSB number

ENG21LA011

Nobody was injured.

An uncontained left engine failure caused by a low cycle fatigue crack that originated from a manufacturing machining groove on the high pressure compressor impeller aft face. Contributing to the incident was service bulletin borescope inspection criteria that was insufficient to detect the presence of machining grooves on the high pressure compressor impeller at the time the incident engine was inspected in May 2004.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

The No. 1 (left) engine high pressure compressor (HPC) impeller developed a low cycle fatigue (LCF) crack that originated from a machining feature (groove) on the aft face of the impeller. The machining groove was created during the part manufacturing process. The LCF crack progressed to overload and resulted in an uncontained HPC impeller failure and secondary impact damage throughout the engine gaspath. Pratt & Whitney Canada (PWC) released a service bulletin (SB) in May 2003 that recommended a one-time borescope inspection of the HPC impeller aft face to check for evidence of machining grooves. The borescope inspection was subsequently mandated by Transport Canada and Federal Aviation Administration (FAA) airworthiness directives (AD). The incident engine was inspected in accordance with the SB inspection instructions in May 2004, with no HPC impeller machining anomalies noted. Following the incident, the HPC impeller fragments were inspected at the PWC facility in Bridgeport, West Virginia in accordance with the overhaul manual procedures. Aside from impact damage created during the incident event, the machining grooves present on the HPC impeller aft face would have passed inspection criteria. It is unlikely the machining grooves would have been visible during the SB borescope inspection performed in May 2004, particularly given the technology available at the time. A crack striation count was performed as part of the materials laboratory analysis of the incident HPC impeller. Assuming each crack striation correlates to one engine cycle, a 1/32 inch crack (thumbnail shape) would have formed on the HPC impeller aft face surface at approximately 1,970 engine cycles. The engine had accumulated 6,803 cycles since new when the HPC impeller borescope inspection was performed in May 2004. The crack would have been detectable by fluorescent penetrant inspection as outlined in the recently released corrective actions discussed in the factual section of this report.

Quoted verbatim from the NTSB record.