Sriwijaya B735 at Jakarta on Jan 9th 2021, lost height and impacted Java Sea

Last Update: May 18, 2021 / 19:17:43 GMT/Zulu time

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Incident Facts

Date of incident
Jan 9, 2021

Classification
Crash

Airline
Sriwijaya

Flight number
SJ-182

Aircraft Registration
PK-CLC

Aircraft Type
Boeing 737-500

ICAO Type Designator
B735

On May 18th 2021 the FAA released their Airworthiness Directive AD-2021-08-14 stating: "This AD was prompted by a flap synchro wire failure that may go undetected by the autothrottle (A/T) computer. This AD requires repetitive BITE (built-in test equipment) tests of the A/T computer to detect a flap synchro wire failure, and corrective action if necessary. The FAA is issuing this AD to address the unsafe condition on these products."

The FAA argued:

The FAA previously issued AD 2000-23-34, Amendment 39-12007 (65 FR 75595, December 4, 2000) (AD 2000-23-34), which applies to all Boeing Model 737-300, -400, and -500 series airplanes, and requires replacing the existing A/T computer with a new, improved A/T computer that included an asymmetric cruise thrust monitor.

On January 9, 2021, a Model 737-500 series airplane operated by Sriwijaya Air was involved in an accident on a flight from Jakarta, Indonesia. There were 62 fatalities. During the ongoing accident investigation, Boeing reported that a flap synchro wire failure may go undetected by the A/T computer on the affected airplanes. Further investigation has revealed that the design update for the A/T computer required by AD 2000-23-34 does not properly account for a possible latent failure of the flap position sensor, which is one data component needed to provide the logic necessary for the asymmetric cruise thrust monitor to operate. Failure of the asymmetric cruise thrust monitor to engage during a large thrust asymmetry event could result in loss of control of the airplane. At this time, the preliminary data of the ongoing accident investigation shows that it is highly unlikely that the accident resulted from the latent failure of the flap synchro wire. However, the FAA has determined that the unsafe condition identified in this AD could exist or develop in Model 737-300, -400, and -500 series airplanes, and that this AD is therefore necessary to address the identified unsafe condition.

The FAA has confirmed that accomplishment of the applicable BITE test in the existing airplane maintenance manual (AMM) detects the flap synchro wire failure. This test is currently not required to be performed repetitively, leading to a potential latent failure if the test is not performed regularly, which will be required by this AD.

Model 737-100 and -200 series airplanes are not affected by this AD due to an A/T design difference that is not subject to the identified unsafe condition.

The AD requires operators to conduct:

Within 250 flight hours or 2 months after the effective date of this AD, whichever occurs first: Perform the applicable A/T computer BITE (built-in test equipment) test, “A/T BITE TEST LRU INTERFACE,” and before further flight do all applicable corrective actions, in accordance with paragraphs 1. through 5. of Boeing Multi-Operator Message MOM-MOM-21-0145-01B(R2), dated March 30, 2021, except as provided in paragraph (h) of this AD. Repeat the test thereafter at intervals not to exceed 2,000 flight hours.
Incident Facts

Date of incident
Jan 9, 2021

Classification
Crash

Airline
Sriwijaya

Flight number
SJ-182

Aircraft Registration
PK-CLC

Aircraft Type
Boeing 737-500

ICAO Type Designator
B735

This article is published under license from Avherald.com. © of text by Avherald.com.
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