Half of the money needed to buy a second air ambulance for London has been pledged by the city's Freemasons.
London's Air Ambulance has £2.35m left to raise after the society said it would offer £2m.
The public has also raised £50,000 after a campaign to raise £4.4m was launched last month.
The Your London Your Helicopter scheme aims to pay for a second helicopter by the end of the summer.
The charity said a second aircraft would provide rapid trauma care for the capital, treating an additional 400 patients annually.
Graham Hodgkin, chief executive of London's Air Ambulance, said: "We have now crossed the halfway mark for the "Your London, Your Helicopter" campaign, thank you to all those who have helped us get there.
"We still have a way to go but I am confident that, with over 10 million people who are passionate about London being the greatest city, we can cross the finish line."
The charity currently has one helicopter but when unavailable there is no other provision.
It flies its current aircraft during daylight hours but last year it was unavailable for 55 days because of maintenance work.
The London Freemasons has appealed to its 40,000 members to fundraise towards its pledge target, £250,000 of which has already been presented to the air ambulance charity.
On the group's website, freemasonry is described as a society of like-minded men who meet regularly in a fraternal and social environment and share a desire to give charitable support to the community.
The group say freemasonry is non religious and non political and is concerned with moral and spiritual values.
London's Air Ambulance facts
- Founded in 1989, it has treated more than 30,000 critically injured people
- It serves the 10 million people who live, work and holiday within the M25
- It operates in partnership with Barts Health NHS Trust and London Ambulance Service
- In 2014 it treated 1,806 patients: 33% from road traffic incidents, 27% from falls and 24% from penetrating trauma including stabbings and shootings
- 2 February 2015
- 5 January 2015
- 22 September 2014
- 9 November 2014
- 9 January 2014
- 25 May 2012