AIRCRASH INVESTIGATIONS - · PDF fileAtlantic Southeast Airlines Flight 529 . ... Powerplant:...

AIRCRASH INVESTIGATIONS

Atlantic Southeast Airlines Flight 529

Reason to be chosen • Flight 529 is one of the only few accidents

arose mainly from maintenance issues.

•We got a few questions in our mind:

→ Are aircrafts precisely designed and these huge birds should not be easily brought down??

→ What contributes to the fatal accident?

→ What sort of things had gone serious wrong??

Goals at the beginning ◆ Investigate the crash deeply

◆ Fully utilize knowledge from lessons

◆ Further develop sense on both aircraft systems and relevant maintenance practices

◆ Build up attention to other air crashes & safety issues

◆ Build up the right attitude towards aircraftmaintenances

About Flight 529

• Date of crash: 21 August 1995

• Operator: Atlantic Southeast Airlines

• Flight no: ASA529

• Atlanta, Georgia to Gulfport, Mississippi

• Aircraft model: Embraer EMB120RT

About EMB-120 Max takeoff weight: 11,990 kg (26,378 lb)

Powerplant: 2× Pratt & Whitney Canada PW118/118A/118B turboprops

Blade Manufacturer: Hamilton Standard

Performance

Cruise speed: 555 km/h (300 knots)

Range: 1,428 km

Service ceiling: 32,000 ft

About Flight 529 – Aircraft Registration: N256AS – Crash site: Carrollton, Georgia – Fatalities: 10

– Injuries: 12

– Probable cause: Mechanical failure

About Flight 529 • Operated by an Embraer 120 turboprop that had

accumulated 18,171 flying cycles.

• Planned flight level: FL240

•When climbing at FL181: several thuds were heard and a propeller blade was later found lost in the No.1 Engine

• No.1 Engine and its nacelle were found deformed and there was leakage of venting oil

After the explosion • The No.1 Engine ran out of torque and soon the aircraft lost

airspeed, bended to the left and pitched down

• Descend rate: 5,500 feet per minute (fpm)

• Crashed into a farmland after airborne for 31 minutes

• All passengers survived the initial impact

• Flame surrounding the cabin killed Captain Ed Gannaway and 8 passengers

Impact on the loss of bladeImpact on the loss of blade •• The engine could not rotate smoothly and evenlyThe engine could not rotate smoothly and evenly

•• An imbalanced force overstressed the engine andAn imbalanced force overstressed the engine and eventually it explodedeventually it exploded

• The outboard frame of the No.1 engine nacelle was deformed and twisted

Impact on the loss of blade • The twisted engine and the three remaining blades were

the key factors of the crash

• The disassembled engine and its retained portion of external metal sheet added frontal drag to the aircraft.

Air particles pass through the nacelle smoothly

Eddy current developed in front of the nacelle, adding drag to the nacelle

Weather Factor

• Clouds: 200ft scatter 3,400ft overcast

• Visibility: 5 miles

• Such low cloud ceiling disabled the flight crews to see the ground clearly

Human Factor • Crew Resources Management CRM was successfully

established

• Pilots were able to carry out emergency procedures

• Cabin crew evacuated the passengers effectively

• Air Traffic Controller provided suitable assistances

• No factor of human error contributes the crash

About the fourth bladeAbout the fourth blade • It was recovered after 1 month • Found in a farmland 35 miles west of the crash site

• Model: 14RF-9 • Manufacturer: Hamilton Standard • Composite- type • Only installed on EMB-120 • Serial No:816398

Initial investigationInitial investigation • Examination in the Material Lab of NTSB

• Long fatigue crack progressed circumferentially fromseveral corrosion pits in the taper bore (錐孔)

• Cracks progressed ¾ of the spar;

• ¼ remained was arose from an overstressing

• Blade fracture contained muddy layers of chloride-deposits

Similar events

• Similar failures were also found prior to this accident. • 2 incidents involving in-flight cracking of Hamilton

Standard propeller blades

• An Inter- Canadien ATR 42 • A Nordests EMB 120

• Chlorine residue on a bleached cork installed in the taper bore to retain the lead balance wool corroded the blade

Responds Hamilton Standard immediate implemented an inspection program to propeller blades in services

A blade fail in the on- wing ultrasonic indication should be removed from services, and

Send to Hamilton Standard for a repair procedure “PS960A”

Wt is PS960A • A standard procedure of inspection & repairing

• Visual inspection • Borescope inspection • Ultrasonic inspection • Replace the bleached cork with a sealant • Blend- repair the blade by sanding

(for spotpeened[珠擊]blade only)

Amendment • Hamilton Standard discovered that some of the return

blades carry no corrosion

• All such blades were shotpeened blade

• In order to reduce working procedures,

• Hamilton Standard management decided the procedure of blending in PS960A could applied to the surroundingsof ultrasonic indication

• Such amendment applied for shotpeened blade only

Internal communication

• The decision was verbally transmitted from the management to the shop technicians

• New implementation received no FAA approval

• The technician was mislead & confused

• He misunderstood that it was acceptable to use PS960A to blend out unexplained ultrasonic indication for both spotpeened and unshotpeened blade

Failures of inspection

• Blade 861398 failed an on- wing inspection on 19 May1994

• Remove from service and sent to Hamilton Standard • It is a unshotpeened blade • PS960A Inspection result:

““No visibleNo visible fa(u)ltsfa(u)lts foundfound……....””

• Later on passed the post-repair ultrasonic inspection

Sanding

• The procedure of sanding itself did not contribute the fatigue

• Sanding mark can cover up the laid crack

Consequences • The rough surfaces in the unshotpeened taper bore

could have scattered and diffused the ultrasonic beam

• Result in reduction in the ultrasonic indication

• Blade 861398 could passed the postrepair inspection

• Accident blade installed on N256AS

• Crack reached critical size and finally flew out duringFlight 529

Recommendations & Improvements • None of an air crash initialed by a single problem • There are always latent hazards

When several failures that linkup together coincidently, they will result in tragedy.

• The aviation industries always learn lessons from air crashes or incidents

• They only expect the failure to be appeared as “the only once”

“…..Better late than never”

• Problem I: Management decision and new procedure was verbally transmitted

•Solution: Revise internal communication and Documentation of engineering decisions. Implementation of new policies or procedures should be officially documented in order to reduce the possibility of misleading and confusion.

Problem II : Shop traveler form shows the accident blade received no final inspection

Solution: To review the necessity of “buy- back” after the repairing to ensure the airworthiness of the blade and thus, improve the stability of the products

Problem III: Technician preformed inspection on the accident blade was transferred from the nickel sheath and fiber glass repair section and only received 90hrs (Standard was 250hrs) training on blade inspection

The blade manufacturer Hamilton Standard should provide enough training on respective post. Technicians should be specialized in a certain maintenance line in order to familiarize their work and enhance the certainly towards the maintenance requirements.

• Problem IV: Atlanta Center controller did not demand emergency services even the pilot requested at the beginning

•Solution: Air Traffic Controller should call for emergency services as soon as possible so as to shorten the time for the rescue team to reach the crash site

• Problem 5: Technicians had not been provided a photograph or model illustrating the appearance of corrosion

•Solution: All the service center technicians were provided with an enlarged color photograph of taper bore corrosion, a model and an instructional video.

Conclusion

• Safety is the key element of aviation

• Simple fault leads to serious disaster

• People in the industries should build up sense of responsibly, precision and caution

• Obey guideline & instruction

We Gain

• By fully utilize knowledge from lessons

• Being emphasized the importance of proper maintenance practice

•• Fortunately, aircraft maintenance standardFortunately, aircraft maintenance standard is keeping in pace with the advancingis keeping in pace with the advancing technology. A safer air travel should betechnology. A safer air travel should be achieved.achieved.

We take opportunity to express our deepWe take opportunity to express our deep sympathy towards the victims of Flight 529sympathy towards the victims of Flight 529

-The End­