There is much discussion about the location of airfields in and around Chelmsford. The big one was off Sandford Road, behind the prison (now, of course, the Springfield Park Estate). There were others at Broomfield Court and Widford Camp.
The debate is over what these airfields were used for, and indeed whether they were airfields at all. In the Official Histories of the War in the Air, Chelmsford gets little mention, other than as a sub-station of the main aerodrome at Chingford. At the end of 1914 there was an order that two aircraft were to be stationed at Chelmsford, as part of the developing anti-aircraft defences on the east coast. But by 1916 this airfield was closed and doesn't appear in subsequent listings of Royal Flying Corps units.
To make sense of the airfield problem it is worthwhile to consider the state of military aviation at the start of the war. Aircraft were flimsy and prone to mechanical failure. Navigation was simple pilotage - following landmarks such as rivers and railway lines at low levels. Airmen in difficulties, whether technical or navigational, needed to be able to put their aircraft down quickly and safely. To do this, the Royal Flying Corps reconnoitred suitable landing grounds and prepared the field for emergency landing. This included mowing and rolling as required (ploughed fields were clearly unsuitable). One requirement was that the field should be approachable from any direction and therefore free from trees and other potential obstructions. In some cases hutted accommodation was provided, with a fuel store. Most importantly there was a telephone.
A pilot getting into difficulties flying from the main base at Sutton's Farm (better known as Hornchurch) to Stow Maries aerodrome (near Maldon) would know the location of these landing grounds and would be able to put down safely and contact his squadron for help.
The east coast air defence system involved night flying and the landing fields would also have flares to help guide airmen back. Note that unlike the second world war there was no formal blackout system, and there are instances of Zeppelin raiders mistakenly bombing the illuminations of the night landing grounds.
The Broomfield Court landing ground (and probably the others) was used for communication. In the absence of radio, signals were conveyed to aircraft by means of coloured panels and strips on the ground during the day, and coloured lights and flares at night.