Civil legislation

One of the great debates in the  in the civilian ex military jet market is what exactly is the legislation regarding use and operation of ejection seats. It would seem that there are no hard and fast rules, and once the aircraft has a certificate announcing its airworthiness the owner can make modifications to the seats to render them non functioning.

It has been quite a battle to find out what exactly can and can't be done but below is the situation so far:

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SAFETY REGULATION GROUP - TECHNICAL PROCEDURES MANUAL
                                                                                                                                               

Db2-2E-2

14 September 2000

EX - MILITARY AIRCRAFT ON PERMIT TO FLY

11.          EJECTION SEATS IN EX-MILITARY PERMIT AEROPLANES

11.1         Introduction

                The purpose of this procedure is to present a set of guidelines to be followed when addressing the approval of aircraft which were operated in military service with live ejection seats. 

The reader is also referred to AMSD TPM E2-E8 covering Aircraft Ejection Seat - maintenance/service information, which describes differences between some seats, and shows typical lives of cartridges.

11.2         Policy

In principle, ex-military aircraft should conform as closely as possible to the standard for which the CAA accepted the service safety record.  This means that ejection seats, canopy jettison systems and MDCs should be maintained “live”, and the CAA recommend that they be maintained thus.

However it is recognised that such charged systems carry an inherent risk and under some circumstances the CAA may be prepared to accept that they be disarmed.  

For the CAA to consider accepting that such systems be disarmed, the aircraft must first be shown to have a landing speed low enough (and with benign handling) that it is reasonable to expect the pilot to be able to make a forced landing in a field.    Although it may be argued that the 61 knot stall speed limit of JAR-23 would provide a criterion consistent with civil codes, this has not been employed in the past.  Examples where disarmed ejection seats have been accepted include:

Type

Threshold speed, knots

Stall speed, knots

Jet Provost Mk 5

90 - 95

73 - 77 gear down, full flap

DH-115 Vampire  

100 knots at typical weight

85 - 95 knots

Aero L-29

86 touchdown

67 - 80 gear down, full flap

These are all aircraft with seats of low capability (not “zero-zero”) which would not work at the critical parts of the flight envelope - immediately after take-off and prior to landing.

Disablement of ejection seats is a modification and as such must be defined (usually via a company procedure) and submitted to the CAA Aircraft Projects Department for approval as a Major modification.   (Form AD282 unless covered as part of the initial investigation.)

11.3         Design Investigation

11.3.1      Aircraft with “Live” seats, Limitations

For aircraft operated with live seats, the appropriate type of seat must be fitted and it must be maintained in accordance with appropriate publications.   These are to be referred (type, manufacturer, serial number, publication) on the AAN approving the aircraft.  

Cartridges powering such seats will be life limited and the lives should be quoted in the AAN.   Manufacturers lives are employed rather than those arbitrarily extended by Eastern Bloc military authorities short of cash.

In the past, no particular attention was paid the occupant weight limitations for ejection seats, but military experience with light/female pilots has shown that it is necessary that such limitations be determined and recorded appropriately.    These limitations must be placarded such that they are clearly visible to the occupant.    The seat occupant weight limitations are to be shown in a Supplement to the Pilots Notes (raised by the E4 Design Organisation) and the AAN will refer to this.

Note 1:  Training of occupants with respect to use of ejection seats is covered under the CAP 632 operational approval.

11.3.2      Aircraft with disabled seats

If disablement of the ejection seats is proposed, it will be addressed as follows.    Simple disarming via removal of explosive charges or cartridges is not sufficient for aircraft capable of aerobatics, as the occupants must be able to abandon such aircraft manually (consistent with JAR 23.807 (d) which requires that it must be possible to abandon the aircraft at all speeds between Vs and Vd).      Aspects to be covered in this event include:

11.3.2.1   Canopy Jettison.   

It is not true that a canopy will always detach unaided under the action of the freestream.    On some canopies the pressure distribution is such that large forces exist at significant forward speeds.  Unless the aircraft Type Design Organisation can give assurances that the canopy will open and jettison freely without the charged system, the system must remain live.   It may be necessary to promulgate a warning to the effect that canopy separation may take a significant time (eg some Jet Provost Mk 5s).

11.3.2.2   Parachute deployment. 

The parachute must remain operable.  The military service disarming procedure does not necessarily address this aspect.    It may be necessary to disconnect parachute withdrawal line from the guillotine in order to ensure that the parachute will completely separate from the seat.  The CAA may require physical demonstration of this.   

This was highlighted in the AAIB investigation following an incident in 1994 when a disabled ejection seat fell out of a Jet Provost during aerobatics.

11.3.2.3   Non-aerobatic Aircraft

If the aircraft is of low enough landing speed and is not to be approved for aerobatics, the ejection system may be disabled without addressing canopy jettison and parachute deployment.   In this instance rapid egress after landing must remain possible, even with total systems failure (ie no electric power available).

11.3.2.4   Placards and Marking

Disabled ejection seats must be clearly placarded as such.  External markings (which may remain for authenticity) should be over-stencilled “disarmed” or “inert” (unless the canopy jettison is cartridge driven and remains live) and seat top boxes painted white.  

NB      At the time of writing (2000) this latter had not yet been adopted as standard, but it is to be promulgated as  a standard by Flight Ops.

11.3.2.5   Pilots Notes/FRCs - Procedure

If ejection seats have been disabled, the procedures in the Pilots Notes (E4 Design company Supplement to be approved by the CAA under AAN) must be address:

- the manual abandonment procedures with any amendments found necessary by the Design Surveyor during investigation.

-  emphasise continued need for checking the integrity of the top latch prior to flight. 

NB This was highlighted in the AAIB investigation following an incident in 1994 when a disabled ejection seat fell out of a Jet Provost during aerobatics.

Flight Reference Cards, if employed, must be similarly amended


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