[6317alan]

Here is the longer version

Partenavia P68B aircraft autopilot and trim systems

Prepared by Alan C Baskett

Introduction
On the 10th July 1978 the Partenavia P68B VH-PNW crashed at Essendon Airport. The Dept in their Special Investigation Report 79-1 of March 1979 list the cause as:

Cause
The cause of the accident was that the aircraft became grossly out of trim at a height, which did not permit time for the crew to affect recovery. The manner in which the out–of–trim condition occurred has not been determined and the possibility of a trim system malfunction cannot be eliminated, however the more likely explanation is that the command trim switch was activated unknowingly.

The coroner at the inquest because of the evidence could not accept the DEPT’s more likely explanation. The DEPT’s simplistic assessment of the cause of this accident is an easy way of minimizing the underlying design deficiencies which allowed the aircraft to “become grossly out-of-trim” and the DEPT’s mismanagement of its certification responsibilities by attempting to shift the cause of the accident to “pilot error”.

This report attempts to detail the history and modifications made to the trim tab travel range of the trim system and the auto- pilot/trim system and of the certification and approval of these modifications.

Summary of events
 
23-1-75  -  First of Type Certification in Australia of P68b Air- craft (no autopilot fitted)
 
April/May - Two P68B arrive in Australia with 1975 Autopilots fitted and no certification.
 
23-5-75 - The Dept formally requests certification justification for Autopilot installation.
12-6-75 - R.A.I. Autopilot Approval - No 124-245-T 1-8-75 to Edo-Aire Flight tested Autopilot
12-9-75 -  R.A.I. Autopilot Approval - No 124-245-T 1-8-75 installation.
 
15-9-75 - Edo-Aire issued S.T.C. no SA 3067SW-D for Auto- pilot/Electric Trim system installation.
 
Sept 75 - Australian approval of Autopilot/Electric trim system installation.
28-4-76 -  Partenavia produce Autopilot flight tests BM 82 and BM 83.
20-7-76 - VH-PNW registered in Australia with TTTR Number 2 fitted.
 
23-11-76 - TTTR Number 2 certified by FAA type data sheet A31 EU Revision 3.
 
16-1-78 - R.A.I. Certify TTTR Number 3 in RAI Type Data Sheet SO / A151 Revision 5
 
10-7-78 - Date of the said Crash.
 
October 78 - S. B. 41 modification to TTTR Number 4.
 
March 79 - Special Investigation Report 79-1 published.
 
17-2-89 - The Dept. flight test P68B aircraft as per CAA document M131-515-4 and in doing so establish TTTR Number5.

NOTE:
FAA  - Federal Aviation Authority (USA)
R.A.I -  The Italian Aviation Authority
STC - FAA Modification certification i.e. Supplementary type Certificate

Partenavia P68B aircraft and autopilot electric trim installation history

The original P68 aircraft and the P68B aircraft were both certified originally with a Trim Tab Travel Range (TTTR ) of 36 degrees.  In fact this was the only trim tab travel range approved in Australia until the requirement for S.B. 41 became a mandatory modification late in 1978 after the accident date.The first P68B aircraft arrived in Australia during 1974 after Forrestair entered into a distribution agreement with Partenavia. This aircraft received “First of Type” certification on 23-1-75 for Australian operation. 

IT  WAS  NOT  FITTED  WITH   AN  AUTOPILOT/ELECTRIC TRIM SYSTEM

During April/early May 1975 two aircraft arrived at Essendon after ferry flight from Italy, both these aircraft were fitted with Edo-Aire Century 111 Autopilot / Electric Trim Systems. During the registration/certification process the Dept. noted the autopilot installation and requested under Reg.27 justification for these non-approved modifications. This justification was first sought verbally and then in writing from the Dept. to Partenavia on the 23-5-75.

In the mean- time Forrestair were required to disconnect and disable the autopilot installations in these aircraft, leaving Forrestair with two aircraft paid for by them but unable to deliver to their customer and receive payment for until completion of the autopilot installation. Partenavia obtained Italian certification from the RAI. for the Autopilot/Electric trim system installation, RAI approval # 124, 245 / T on the 12-6-75 more than a month after the two aircraft had arrived in Australia after the ferry flight from Italy.

I am unaware of any flight test data or any justification for the Italian certification of the Autopilot/Electric trim system being submitted to the RAI for this certification.  Note: None was produced during legal discovery for the litigation by Partenavia to me and this was the process where Partenavia were legally required to produce all documents that we had requested. 

Italian certification of the Autopilot/Electric trim system would have been a prerequisite for testing to obtain American STC approval of this modification. 

I suspect that Edo-Aire were probably mislead into a false sense of security when conducting the flight tests for the STC issue as the aircraft had already obtained Italian certification. Partenavia may have led Edo-aire into believing that an aft C of G may have been the critical condition to be tested. It appears that this is the only condition where results appear to be satisfactory can obtained.

Edo-aire document A75-66SW-DAS is incomplete, inadequate, superficial and misleading for the following reasons:

       1; The section of the FAA Flight Test Report Guide Form 811018(6.75) dated June 1975 on pages 69 and 70 referring to Electric Trim System including flight tests have not been reported on.

       2; The only flight tests conducted at forward C of G position were function tests only

      3; Autopilot malfunction and trim runaway tests were all conducted at aft C of G position only. This is not a normal operating condition for the P68B aircraft as even at all up weight the C of G position is normally towards the forward limit.  Note: On the night of the accident VH-PNW operating weight was only 57 kg below the maximum allowable operating weight, at a C of G position only six percent aft of the forward position of the total allowable.

   4; Trim runaway tests were not conducted hands free but “Stick force observations were made without allowing an aircraft or air- speed change to occur”

   5; Trim runaway tests were not conducted in takeoff or climb configurations

   6; Trim runaway tests were not conducted to determine if a temporary force of 50 pounds (22.65kg) on the elevator control was exceeded when corrective action is not initiated until the malfunction is detected by the pilot for the following time delays and conditions of flight:

Takeoff, climb, approach & landing - 2 seconds

Cruise - 4 seconds

7; The most critical weight and C of G condition was not determined and used for trim runaway tests. However the FAA- STC No SA 3067 SW-D was issued by Edo-aire on the 15-9-75.

The Australian Dept. then approved the Autopilot / Electric trim system modification to the P68B for use in Australia even though they did not then or even now receive any flight test data from Partenavia to justify this Australian certification as required by ANO 101-22-7.3(6) 

They do not even have a copy of the S.T.C.

The Dept. did not require Partenavia to submit any evidence “relating to the design to which the application relates including evidence of the effect of the design on safety of an aircraft” as required by ANR.40 (1 )( 2 )

The Dept. had previously recognized that the possibilities of problems occurring with aircraft designed and manufactured in counties other than the USA or the UK as they had included in ANO 101-22.1.2:

“The Director-General may specify additional design standards, documents and other evidence for aircraft types other than those designed in the United Stares of America or the United Kingdom.”

I have not been able to discover any such additional require-ments being made for the certification of the P68B or its modification by installing the Autopilot / Electric trim system. In fact when one departmental officer suggested additional flight tests for the first of type certification, he was informed that under no circumstances would this be required (copy of departmental memo held) nor was any additional requirement made for the certification of the Autopilot/Electric trim system. In fact the reverse is the case as the Autopilot/Electric trim system was certified with the requirements being less than that required by the statuary standards.

    So the Autopilot /Electric trim system was certified in Australia.

Partenavia produced flight tests numbered BM82 and BM83. These tests are dated 28-4-76 and are similar in nature to Edo-Aire flight tests

BM 82 and BM 83 and Edo-Aire document A75-66SW-DAS are all documents applicable to the Autopilot / Electric system installation certification none of which are in possession of the department.

During April 1976 Forrestair took delivery of VH PNW. This aircraft Partenavia claim and the wreckage reconstruction would support this claim, was fitted with trim tab travel range number two of 28°. This TTTR not certified in Australia and the change was not noticed during the certification process by the department,  nor was it noted during subsequent maintenance by Forrestair or Phil White (Aircraft Maintenance Engineer). The only certification details of this change to TTTR 2 are included in FAA types certificate Data Sheet A31EU Revision 3 (dated 23/11/76) more than six months after installation in VH-PNW.

No justification have been discovered to myself or to the department and for this modification.

A further modification of the trim tab travel range (TTTR number three) was approved by the R.A.I. on the 16th of the first 1978 in R.A.I. type certification data sheet SO/A151 revision five. This reduced trim tab travel range to 24°.

Again this modification has no design justification or flight tests discovered by Partenavia to myself, nor were any submitted to the Department. Partenavia were either unaware; or are unable; or unwilling to notify certification authorities of changes to the P68B design status and obtaining approval before incorporation into production aircraft.

These modifications to the Trim Tab Travel range from 36° to 28° indicate that Partenavia were aware that a problems existed in the trim system.

Perhaps the events of the 10th of July 78 may have been averted at the modifications to 24° total travel had been incorporated into Australian aircraft as this reduced the nose-down trim capability by 54% from a total excess on over 140% to only 86% of excess capabilities.

After the crash of VH-PNW on the 10th July 1978, Partenavia issued Service Bulletin 41 during October 1978, which changed trim tab travel range (TTTR number four) to 14° and again Partenavia have not discovered to me any design justification or flight tests to support this modification. Neither have they provided any design justification or flight tests to the Department.

The departments CAA report M131-515-4, I submit is the only fight test report that is available - even though it would not be produced until early 1989 - that is able to establish the actual trim tab travel required for the Partenavia. Even though its primary purpose was to determine the P68.B’s compliance - with F.A.A.23-689 (f) - by doing this the Department has established the trim tab travel requirements for the P68B. By logical conversion as detailed in TTTR number 5, it can be determined that only 7 ½ degrees of total trim travel is required for the aircrafts safe operation.

Trim Trim Tab Travel Diagram

Trim tab travel range number one
0 degrees + / – 1 degree Down To 16 degrees + / – 1 degree UP
 

- This was the only range that was certified in Australia
- This range is shown on the Trim Tab Travel Ranges drawing - colored RED .

- This travel range has an excess nose down trim capability of 18.5 degrees or 246 %excess capability.
- This travel range has an excess nose up trim capability of 10 degrees or 135 % excess capability.
- This excess capability has been calculated over that shown in Trim Tab Travel Range number 5
{Comment: No design justification for this trim tab travel range - by the Dept, or Partenavia - has been discovered by the author A Baskett.}

Trim tab travel range number two
20 Degrees + / – 1 Degree Down - To 8 Degrees + / – 1degree Up
 
- This range is shown on the Trim Tab Travel Ranges drawing as being coloured YELLOW.
- This is the range that was approved and certified by the F.A.A Type Certificate Data Sheet A31EU Revision 3 dated 23/11/76.
- This range was not approved in Australia.
- This is the  range  that  Partenavia  claim  was  fitted  to VH-PNW.
- This appears to be the range fitted to VH-PNW as far as can be determined by the wreckage reconstruction.
- This travel range has an excess nose down capability of 10.5 or 140% excess capability.
- This excess capability has been calculated over that required in Trim tab travel range Number 5.
{Comment: No design justification for this trim tab travel range - by the Dept, or Partenavia - has been discovered by the author A Baskett.}

Trim tab travel range number 3
20 Degrees +/- 1 degree   to 4degrees +/- 1 degree Down
 
- This range is shown on the Trim Tab Travel Range drawing as being coloured BLUE.
- This is the range that was approved and certified by the R.A.I. Type Certificate Data Sheet SO/A151 Revision 5 dated 16/1/78.
- This Range was not approved in Australia.
- This travel range has an excess nose down trim capability of 6.5 degrees or 86% excess capability.
- This travel range has an excess nose up trim capability of 10 degrees or 135% excess capability.
- This excess capability has been calculated over that required in Trim tab travel range Number 5.
 {Comment: No design justification for this trim tab travel range - by the Dept, or Partenavia - has been discovered by the author A Baskett.}

Trim tab travel range number four
1 degree Down to 15 degrees Down 

- This range is shown on the Trim Travel Range drawing as being coloured ORANGE

- This is the range that has been approved by the requirements to incorporate Partenavia Service Bulletin 41 in October 1978.

- This range is now approved in Australia.

- This travel range has an excess nose down trim capability of 1.5 degrees or 22% excess capability.

-This travel range has an excess nose up capability of 5 degrees or 66% excess capability.

- This excess capability has been calculated over that required in trim tab travel range Number 5.

{Comment: No design justification for this trim tab travel range - by the Dept, or Partenavia - has been discovered by the author A Baskett.}

Trim tab travel range number five
2.5 degrees Down to 10 degrees Down

- This range is shown on the Trim Tab Travel Ranges drawing as being coloured GREEN.

- This is the range discovered to A Baskett to be approved by the Dept. in C.A.A. document M-141-515-4 dated 17/2/89.

- This range is NOT approved in Australia.

- This travel range was established by flight test procedures to confirm compliance with F.A. R. 23-689(f) by a correctly rigged P68B aircraft at both forward and aft loading conditions, in so doing the total trim tab travel range required was also established for the Partenavia P68B.

(Note: The method of determining the angular travel – was by dividing the 14 degrees of travel of a correctly rigged aircraft by the number of divisions of travel indicated by the trim indicator i.e. 8.5 degrees. Therefore 1 division of trim indicator equals 1.65 degrees trim indicator scale.of trim tab travel. It is assumed linier along the scale.)
{Comment: The M-131-515-4 document is the only document available that the author, A Baskett, has been able to discover that has any creditability to establish the actual trim tab travel requirement for the Partenavia P68B Aircraft.}

Special investigation report 79-1

This Accident Investigation Report prepared by the Dept while appearing to be extensive and detailed in its investigation of this accident is in fact deficient in its pursuit of the subject matter to its logical extension of the ramifications of the total assessment of all the facts.

The Dept have touched on the matter of pilot strength when they investigated control system failure caused by pilot input loads but chose to not detail in a similar manner the requirements of FAR 23-143© which limit the force required to be exerted by a pilot on a temporary basis not to exceed 75 pounds.

This report also omits to detail any reference to the fact that the position of the trim tab actuator was in a position that indicatedthat the trim tab travel was other than that certified in Australia.

This report omits to admit to the fact that the Dept failed to obtain flight test reports as required by ANO 101-22 prior to certifying the Autopilot/Electric Trim system.

This report omits to detail that the Trim Tab Travel Range was excessive to that required to comply with FAR23-689(f) which establishes total trim capacity required for an aircraft.

This report fails totally to address the fact that the Electric Trim Systemwas never flight tested correctly as required.

This report by not completely investigating all aspects of the ElectricTrim System was able to minimize the design and certification deficiencies to enable the claim of pilot error to be raised by stating - “However, the more likely explanation is that the command trim switch was activated unknowingly.”

This cannot be supported by any evidence as the coroner found at the inquest.

The CAUSE as listed in this report is incorrect and misleading and would be more accurate if listed similar to the following:

Cause

The cause of the accident was that the aircraft became grossly out of trim at a height  which did not permit time for the crew to affect recovery. The trim system design allowed control forces to be generated that exceeded pilot control force limits to be exceeded by a substantial amount. The manner in which the out of trim condition occurred has not been determined and the possibility of a trim system malfunction cannot be eliminated.

Footnote.

I have no beef with the actual accident investigators Stewart or Jim, only the executive above them. At the time of the accident BASI were part of the Department and it appears that nothing has changed over 37 years. From what I can see, I am glad I am not involved in General Aviation in today’s environment.
 
 Alan C Baskett