AEM                        Phenolic vapours (another packing hazard)    (Updated on 27 Aug 2006)

Whilst working at Addlestone for Plessey Displays, the company were producing huge printed-circuit boards.  The printed wiring was designed to act as a microwave device that fed out signals to different ports in various phase configurations.  The different ports were connected to different parts of the Instrument Landing System (ILS) aerial  to provide signals that allowed an incoming aircraft to know its position with respect to a centre line of the runway, that was the perfect position to put the aeroplane down.  The maths get quite hairy and is outside my capability.  The huge printed circuit boards were enclosed within a weatherproof metal case that had a number of coax connectors so that the interconnecting cables could feed different phase signals to different parts of the aerial system.

Plessey made a number of these Aerial Distributors for British Airports Authority (BAA).  Besides making enough devices for fitting to airfields within the BAA empire, a few spares were made and held in a stores at Prestwick.  These spares were securely boxed so that they could be rapidly moved from the store when (not if) an aircraft overran the runway and damaged the Aerial Distributor.

The inevitable happened and BAA took one of the boxed spares  to the airfield where an aircraft had pranged a Distributor.  They opened the box and were most dismayed at what they found.  A totally corroded wreck.  Of course a lot of recrimination and tough thinking.  It was deduced what had happened.

The Distributor was placed inside a pine case and the outside of the case was sealed with bituminised paper making the enclosure more or less airtight.  But what nobody had thought about was that pine timber exudes resin and the resin in turn exudes phenol in vapour form   And tin, copper, and fine solder corrode in the presence of phenolic vapours

What Plessey should have done was to seal the Distributor and then box it, making sure that the box had sufficient ventilation to allow the vapours to dissipate into free air.  Plessey did exactly the wrong thing by containing the vapours against the Distributor.  But "learning the hard way" is common in industry and politics;  look at 9/11 for an example

If you haven't already looked at my other packing story, click on the link for page AEL.