DOCUMENT TYPE AND REF No TECHNICAL NEWS SHEET CT (MOTH) No 33 Issue 1
 

TITLE: COCKPIT SAFETY HARNESS INSTALLATION - INTEGRITY AND LIFING

CLASSIFICATION MANDATORY

PLANNING INFORMATION
Effectivity

All variants of DH60, DHBOG, DH60M, DH60X, DH82, DH82A, Queen Bee, DH83 and DH94 aircraft.

Reason

During the investigation into a recent aircraft accident the attachment of the right hand front cockpit shoulder harness restraint cable failed during impact. In the rear cockpit the shoulder restraint cable had broken at its mid point. Also, the right hand lap strap had torn completely through, close to a stitched joint that attached one of the leather reinforcing straps.

Additionally, it was determined that the front and rear cockpit safety harnesses were originally designed to be worn in conjunction with a military pattern seat-type parachute. When used without the seat-type parachute the safety harness fails to meet the requirements of Air Ministry Design Leaflet E3. Moreover, in this and other accidents, it was noted that although the safety harnesses fitted to the aircraft did not appear to be in a significantly deteriorated condition, the webbing had actually lost between 50 and 75% of its strength.

Advisory TNS CT(Moth) No 12 Issue 1, dated 30 January 1990, (cancelling TNS CT(82) No 12 Issue 2 dated 1 June 1964) required operators to establish that the front cockpit shoulder harness attachment bracket securing bolts were made from High Tensile Steel. A 50-hour check for corrosion of the attachment brackets was also introduced.

Description
Part A of this TNS CT(Moth) No 33 Issue 1, requires all operators of DH60, DH60G, DH60M, DH60X, DH82, DH82A, Queen Bee, DH83 and DH94 aircraft to establish the integrity of the front and rear cockpit shoulder harness installation in their aircraft. This check is to be carried out within 10 flying hours or 3 months from the date of issue of this TNS, whichever occurs first. Thereafter, Part B of this TNS CT(Moth) No 33 Issue 1 is to be carried out at the next and every subsequent Annual Check. Finally, Part C of this TNS CT(Moth) No 33 Issue 1 introduces a formal lifing policy for the front and rear cockpit safety harnesses and gives advice on better husbandry of the harnesses.

This TNS CT(Moth) No 33 Issue I consolidates other TNS requirements affecting the cockpit safety harness installation and supersedes TNS CT(Moth) No 12 Issue 1.

Compliance
The Accomplishment Instructions contained in this TNS CT(Moth) No 33 Issue 1 have been classified as MANDATORY by the United Kingdom Civil Aviation Authority.

The checks called up at Part A, Paragraph 2A and 2B of this'TNS CT(Moth) No 33 Issue 1 are to be carried out within 10 flying hours or within three months from the date of issue of this TNS, whichever comes sooner.

Thereafter, the checks called up at Part B, Paragraph 2C of this TNS CT(Moth) No 33 Issue 1 are to be carried out at the next and all subsequent Annual Checks.

Part C, Paragraph 2D dthis TNS CT(Moth) No 33 issue 1 introduces a formal lifing policy for the front and rear cockpit safety harnesses. To allow time for the procurement of supplies of new safety harness assemblies, the installed life Limitation is to be implemented not later than 150 flying hours or three years from the date of issue of this TNS, whichever comes sooner.

The Type Design Authority notes that the safety harness fails to meet the requirements of Air Ministry Design Leaflet E3 when military seat-type parachutes are not used. It is strongly recommends that owners or operators consider fitting their aircraft with a harness of improved design made from modern materials meeting the requirements of Air Ministry Design Leaflet E3.

Approval

The contents of this TNS have been approved under the authority of the United Kingdom Civil Aviation Authority approval reference DAI/9402/92.

References

TNS CT(Moth) No 12 Issue 1.

Air Registration Board (ARB) Civil Aircraft Inspection procedure (CAIP) Leaflet AL/3-11, Issue 1 dated 1 November 1971: Aircraft Systems and Equipment - Safety Belts and Harnesses (Obsolete).

Air Registration Board (ARB) Specification No 4, Issue 2 dated 1 February 1962 - Safety Harnesses (Obsolete).

Publications Affected
The appropriate de Havilland Moth Maintenance and Repair Manual.

British Aerospace TNS Series CT (Moth).

Material Information
 

	DH82, DH82A and Queen Bee
ITEM	PART NO.	QTY
Bolt, 90° csk head (Alternative Bolt, 90° csk raised head)	AS1242-10C (AS1244-10C)	4 (4)
Washer, Plain	SP13C	4
Stiffnut, thin	AGS 2002C1	4

	DH94
ITEM	PART NO.	QTY
Bolt, hex head	A25-10C	8
Washer, plain	94A3	8
Washer, spring	SP55/C	8
Stiffnut, thin	AGS 2002C1	8

	NON AEROBATIC LAP STRAPS
LAP STRAPS	PART NO.	QTY	DH MOTH APPLICABILITY
Front & Rear cockpit	H37544	2	DH60G, DH60M & DH83
Front & Rear cockpit	94F155	2	DH94

ACCOMPLISHMENT INSTRUCTIONS
Work Required, Part A - Integrity Check (all aircraft). Within 10 flying hours or three months from the date of issue of this TNS, whichever comes sooner:
Gain access to the front and rear cockpit shoulder harness attachment brackets.

Using a suitable light source, mirrors, magnifying glasses or other visual aids, examine each attachment bracket, its securing bolts, saddle washers and the fuselage frame in the vicinity for evidence of cracking, corrosion, wear or deterioration of the surface finish. Any faults revealed by this check are to be rectified in accordance with the requirements of the appropriate de Havilland Moth Maintenance and Repair Manual.

Examine the front and rear cockpit shoulder harness restraint cables throughout their length, especially for fraying and signs of wear caused by contact with the harness holder plates. Where there are signs of wear, or failure of the strands of the cable, the cable is to be replaced.

Without removing the safety harnesses from the aircraft, each individual strap of the safety harnesses in both front and rear cockpits are to be examined in detail for evidence of:

1. Broken stitches
2. Cuts and tears
3. Chafing
4. Signs of contamination due to acid, oil, grease and water
5. Deterioration due to exposure to sunlight
6. Security of the end fittings
7. Signs of excessive wear or elongation of the attachment holes.
Where any signs of deterioration are found, the safety harness is to be replaced before further flight.
Work Required, Part A - Integrity Check (DH82 and DH82A Front Cockpit and DH94 Front and Rear Cockpit only)
Locate the two attachment brackets in each cockpit. Visually examine the heads of the two securing bolts in each attachment bracket to ensure that they are manufactured from High Tensile Steel. High Tensile Steel bolts may be identified by a dimple in the head of the bolt. Low Tensile Steel bolts do not have any identification.

NOTE: It may be necessary to gain access through the fuselage fabric to accomplish this check

Where High Tensile Steel bolts are not fitted, the following action is to be taken before further flight:

Remove and discard the Low Tensile Steel 2BA bolts securing the attachment brackets.

Examine the brackets for condition, especially corrosion and condition of the surface finish. Where necessary, treat any corrosion and restore the surface finish in accordance with the appropriate de Havilland Moth Maintenance and Repair Manual.

Using an approved jointing compound, refit the attachment brackets using High Tensile Steel bolts.

Restore the fuselage fabric and aircraft paint finish in accordance with instructions contained in the appropriate de Havilland Moth Maintenance and Repair Manual.

Work Required, Part B - Repeat Applications (all aircraft). At the next and subsequent Annual Check:
Examine the front and rear cockpit shoulder harness attachment brackets in accordance with Paragraph 2A(2).

Examine the front and rear cockpit shoulder harness restraint cables in accordance with Paragraph 2A(3).

Examine the front and rear cockpit safety harness straps in accordance with Paragraphs 2A(4) and 2A(5).

Work Required, Part C - Introduction of Lifing Policy With effect from the date of issue of this TNS:
An installed life of 9 years from the date of initial fitment is introduced for the front and rear cockpit safety harnesses.

If it is not possible to determine from the aircraft technical records the date of initial fitment of the front and rear cockpit safety harnesses, they are to be replaced not later than 150 flying hours or 3 years from the date of issue of this TNS CT (Moth) No 33 Issue 1, whichever comes sooner.

Aircraft owners and operators should note that the integrity of the cockpit safety harnesses can be ensured by the use of careful husbandry. The adoption of basic measures such as the use of cockpit covers to shield the harnesses from exposure to sunlight and care being taken to avoid contamination by acid, oil, grease and other substances will greatly enhance the longevity of the harnesses.

Work Required - Manuals

For all affected aircraft types, amend the Recommended Maintenance Schedule to add the requirements of this TNS CT(Moth) No 33 Issue 1, Paragraphs 2C and 2D.

RECORDING
Record compliance with this TNS CT (Moth) No 33 Issue 1, together with the date and flying hours accomplished, in the aircraft technical records.

Whenever a TNS is issued or amended, operators are required to hand amend the copy they hold of TNS CT (Moth) No I, "LISTING OF TECHNICAL NEWS SHEETS" to ensure an up-to-date listing is maintained. The following annotations should be made in TNS CT (Moth) No 1:

TNS CT(Moth) No 12 Issue 1; Superseded by TNS CT(Moth) No 33 Issue 1.

Add "TNS CT(Moth) No 33 Issue 1, Cockpit Safety Harness Installation - Integrity and Lifing" to the list.

REPORTING

All cases of equipment failure found during satisfaction of this TNS CT(Moth) No 33 Issue 1 are to be reported to the aircraft Type Design Authority. When reporting details of faults found or in cases where technical advice is required, contact:

 

The Engineering Support Manager

British Aerospace Aerostructures Ltd

Military Business Unit

Chadderton Works

Greengate

Middleton

Manchester

M24 1 SA	Telephone:	+44 (0)161 955 8789
ENGLAND	Fax:	+44 (0)161 955 8798

E3
This sheet re-issued November, 1937,
with A.L. No. 1 to A .P. 1208.

DESIGN LEAFLET E.3

ACCESSORIES

INSTALLATION OF SAFETY HARNESS, SAFETY BELTS, AND LAP STRAPS

General.--The circumstances in which safety harness, safety belts, and lap straps are to be fitted are specified in the Air Navigation (No. 2) Regulations, 1937. The present leaflet deals only with the method of installing safety harness, safety belts, and lap straps in an aero- plane. Requirements for the harness, belts, and straps themselves are given in Civil Specification No.12B.

Safety harness.--The harness must be installed so as to keep the wearer firmly in his seat when experiencing forces of 850 lb. tending to throw him forwards and 850 lb.* tending to throw him upwards, acting separately. (These forces represent accelerations of 5g forwards and upwards on a person weighing 170 lb.) A factor of at least 1.0 is required on the harness, its attachment fittings, and the main structure of the aeroplane in the neighbourhood of the attachment fittings. The factor on the harness is to be based upon the certified strengths marked on the component straps in accordance with Civil Specification No.l2B.

Safety belt.--The belt must be installed so as to keep the wearer in his seat when experiencing forces of 850 lb. tending to throw him forwards and 510 lb.+ tending to throw him upwards, acting separately. (These forces represent accelerations of 5g forwards and 3g upwards on a person weighing 170 lb.) A factor of at least 1.0 is required on the belt, its attachment fittings, and the main structure of the aeroplane in the neighbourhood of the attachment fittings. The factor on the belt is to be based upon the certified strength marked on the belt in accordance with Civil Specification No. 12B allowance being made for the catenary of the belt when being worn by an average person.

Lap strap.--The lap strap must be installed so as to keep the wearer in his seat when experiencing an upward force of 250 lb.* A factor of at least 1·0 is required on the strap, its attachment fittings, and the main structure of the aeroplane in the neighbourhood of the attach- ment fittings. The factor on the strap is to be based on the certified strength marked on the . strap in accordance with Civil Specification No· 12B, allowance being made for the catenary of the lap strap when being worn by an average person.

Parachute seats.--If parachute seats are fitted, and if the harness, belt, or lap strap is attached to the seat, then the attachments of the seat to the aeroplane structure must be stronger than the attachments of the harness, belt or strap to the seat. This is in order that there may be no chance of the seat and parachute breaking adrift together in such.a way as to prevent the parachute being used.

* This is the resultant upward force, i.e.. the weight of the pilot is not to be subtracted from this force. (385273