A falcon 20 in cruise at FL330 noted slight yaw. On start of descent noted yaw in opposite direction...

Attributes
ACN	568957
Time
Date	200212
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : zzz.airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Make Model Name	Falcon 20FJF/20C/20D/20E/20F
Operating Under FAR Part	Part 91
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company other
Qualification	pilot : atp pilot : multi engine
Experience	flight time last 90 days : 90 flight time total : 4000 flight time type : 90
ASRS Report	568957
Person 2
Affiliation	company other
Function	flight crew : captain
Qualification	pilot : atp
Experience	flight time last 90 days : 267 flight time total : 3596 flight time type : 1735
ASRS Report	568952
Events
Anomaly	aircraft equipment problem : critical maintenance problem : improper maintenance non adherence : far non adherence : published procedure
Independent Detector	other flight crewa other flight crewb
Resolutory Action	none taken : detected after the fact
Consequence	other other other
Factors
Maintenance	contributing factor : schedule pressure performance deficiency : unqualified personnel performance deficiency : training performance deficiency : inspection
Supplementary
Problem Areas	Flight Crew Human Performance Company Aircraft Maintenance Human Performance
Primary Problem	Maintenance Human Performance

Narrative:

I arrived at the airport at xa:30 dec/wed/02. I went to the aircraft to do a preflight inspection. It had snowed all day and there was about 2 in of snow on the aircraft. Since I was substituting for the normal first officer and not being familiar with normal procedures on this schedule run I asked the mechanic what the normal procedures were. He informed me that normal protocol was to leave the engine plugs in so the engines could be preheated. Normally, I would take the plugs out, pitot covers off, check the gas caps, check the oil, etc, and do a normal preflight. The mechanic informed me that he had added 2 pints in the #2 engines and 1 pint in the #1 engine, so I did not check the oil. I did a preflight and 'looked' at the cowl latches noticed that they were closed. The mechanic informed me that he would pre-heat the engine and I would unload the 1ST truck and then do cockpit set up while the captain unloaded the 2ND truck, so that's what I did. The mechanic finished the outside preflight and removed the plugs and pitot covers. We then started the engine and taxied to the deicing equipment to deice the airplane. We departed around xb:30 local on runway 13 and climbed and FL330. Cruising at FL330 on autoplt we did paperwork. About 1/2 to destination we heard thump and the aircraft yawed to the right. The captain took control while we assessed the situation. The airplane flew fine and engine parameters were good. We conclude the control surface or connection had a buildup of ice and broke loose so we continued flight. Upon descent into airport we hear another thump and the aircraft yawed to the left. Again engine instruments indicated good and we did a normal approach and landing. Arriving at the ramp we inspected the aircraft and found the #1 engine lower and inboard cowling ajar, and the #2 lower outboard cowling missing. Callback conversation with reporter revealed the following information: the reporter stated when investigating the cause of the damaged #1 engine lower cowling and the loss of the #2 engine lower cowling it was discovered that the lower cowling must be closed and latched in a precise sequence. The reporter said the lower cowling has three latches and the center latch must be closed first since it has a centering pin that aligns all the latches. The reporter stated closing the cowling in any other sequence will not allow positive locking even though the latches appear locked.

Original NASA ASRS Text

Title: A FALCON 20 IN CRUISE AT FL330 NOTED SLIGHT YAW. ON START OF DSCNT NOTED YAW IN OPPOSITE DIRECTION. ON LNDG FOUND #1 ENG LOWER COWLING OPEN AND #2 ENG LOWER COWLING MISSING.

Narrative: I ARRIVED AT THE ARPT AT XA:30 DEC/WED/02. I WENT TO THE ACFT TO DO A PREFLT INSPECTION. IT HAD SNOWED ALL DAY AND THERE WAS ABOUT 2 IN OF SNOW ON THE ACFT. SINCE I WAS SUBSTITUTING FOR THE NORMAL FO AND NOT BEING FAMILIAR WITH NORMAL PROCS ON THIS SCHEDULE RUN I ASKED THE MECH WHAT THE NORMAL PROCS WERE. HE INFORMED ME THAT NORMAL PROTOCOL WAS TO LEAVE THE ENG PLUGS IN SO THE ENGS COULD BE PREHEATED. NORMALLY, I WOULD TAKE THE PLUGS OUT, PITOT COVERS OFF, CHECK THE GAS CAPS, CHECK THE OIL, ETC, AND DO A NORMAL PREFLT. THE MECH INFORMED ME THAT HE HAD ADDED 2 PINTS IN THE #2 ENGS AND 1 PINT IN THE #1 ENG, SO I DID NOT CHK THE OIL. I DID A PREFLT AND 'LOOKED' AT THE COWL LATCHES NOTICED THAT THEY WERE CLOSED. THE MECH INFORMED ME THAT HE WOULD PRE-HEAT THE ENG AND I WOULD UNLOAD THE 1ST TRUCK AND THEN DO COCKPIT SET UP WHILE THE CAPT UNLOADED THE 2ND TRUCK, SO THAT'S WHAT I DID. THE MECH FINISHED THE OUTSIDE PREFLT AND REMOVED THE PLUGS AND PITOT COVERS. WE THEN STARTED THE ENG AND TAXIED TO THE DEICING EQUIP TO DEICE THE AIRPLANE. WE DEPARTED AROUND XB:30 LOCAL ON RWY 13 AND CLBED AND FL330. CRUISING AT FL330 ON AUTOPLT WE DID PAPERWORK. ABOUT 1/2 TO DESTINATION WE HEARD THUMP AND THE ACFT YAWED TO THE R. THE CAPT TOOK CONTROL WHILE WE ASSESSED THE SIT. THE AIRPLANE FLEW FINE AND ENG PARAMETERS WERE GOOD. WE CONCLUDE THE CTL SURFACE OR CONNECTION HAD A BUILDUP OF ICE AND BROKE LOOSE SO WE CONTINUED FLT. UPON DSCNT INTO ARPT WE HEAR ANOTHER THUMP AND THE ACFT YAWED TO THE L. AGAIN ENG INSTRUMENTS INDICATED GOOD AND WE DID A NORMAL APCH AND LNDG. ARRIVING AT THE RAMP WE INSPECTED THE ACFT AND FOUND THE #1 ENG LOWER AND INBOARD COWLING AJAR, AND THE #2 LOWER OUTBOARD COWLING MISSING. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED WHEN INVESTIGATING THE CAUSE OF THE DAMAGED #1 ENG LOWER COWLING AND THE LOSS OF THE #2 ENG LOWER COWLING IT WAS DISCOVERED THAT THE LOWER COWLING MUST BE CLOSED AND LATCHED IN A PRECISE SEQUENCE. THE RPTR SAID THE LOWER COWLING HAS THREE LATCHES AND THE CENTER LATCH MUST BE CLOSED FIRST SINCE IT HAS A CENTERING PIN THAT ALIGNS ALL THE LATCHES. THE RPTR STATED CLOSING THE COWLING IN ANY OTHER SEQUENCE WILL NOT ALLOW POSITIVE LOCKING EVEN THOUGH THE LATCHES APPEAR LOCKED.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

A falcon 20 in cruise at FL330 noted slight yaw. On start of descent noted yaw in opposite direction. On landing found #1 engine lower cowling open and #2 engine lower cowling missing.