SERVICE IMPACT POSTMORTEM
Underpanel failure, 20 May 2007
Primary responding SRE: mikeyd
Prepared by: mikeyd

SUMMARY

Insufficient reinforcement across leading edge of JTD aluminum underpanel caused it to tear loose at highway speeds. Leading edge grinding into pavement quickly led to catastrophic failure, resulting in total destruction of the underpanel and a short but dangerous trip interruption.

TIMELINE

All times approximate, in PDT.

12:12, US 101N at CA84/Marsh Rd: Sudden noise and vibration alert driver and passenger to initial panel detachment.

12:15 Car stopped on narrow shoulder of US101 between traffic and sound wall. Inspection finds panel loose in center, but still fully attached at all screws, and panel does not touch pavement when at rest. mikeyd decides to try to remove car from freeway before attempting panel removal.

12:21 Car back in motion at about 40mph, panel again scrapes ground under wind stress. Less than 1min later, total collapse of panel is indicated by suddenly increased noise and vibration, sparks, and impaired steering.

12:25 Again stopped on freeway shoulder, panel is found torn into two pieces, with larger piece crushed under forward engine brace. Escalation to tow truck/AAA is considered (sooyeonk) but argued unnecessary (mikeyd). After jacking the car from front passenger lift point, the remaining fasteners are removed using factory tool kit and panel breaks loose.

12:50 Panel removed, visual inspection finds no obvious damage to belts, radiator, or tires. Car returned to service.

14:50 SRE monitors tire and oil pressure for 2h before declaring resolution.

IMMEDIATE CAUSE

Insufficient attachment at front center of aluminum panel caused it to flex under strong wind (vehicle speed of ~80mph + wind gusts of 30mph) and break free of containing bumper lip. Sustained wind overload then pressed leading edge of panel into pavement, shortly leading to catastrophic failure.

CONTRIBUTING FACTORS

Panel purchased used, without mounting instructions. Either the missing documentation does not call for drilling extra attachment points, or the previous owner also had it installed incorrectly.

Panel installation did not undergo production launch review due to unavailability of key engineer (laz).

Initial judgement to attempt to drive car off freeway with panel loose was poor. At first stop (12:15), panel was in salvageable condition. At second stop (12:25), panel was clearly destroyed (see photograph).

USERS AFFECTED

2: me and Soo. Travel to Daly City delayed by ~25m. Effects on passing traffic on 101N not monitored, but did not appear to be serious.

FINANCIAL IMPACT

Total loss of underpanel, $100. Bumper and mating plastic components damaged but still usable ($350).

ACTIONS

Renew recently expired AAA membership.

Evaluate whether to install a third panel. If doing so, drill and attach several points well in excess of manufacturer's specifications.

27 May 2007 02:10 PT - persistent link - trackback - 3 comments