The number of passengers travelling through Heathrow last month was down by around 97% compared with April 2019, the airport has announced.
It expects passenger demand will "remain weak" until governments around the world "deem it safe to lift travel restrictions".
Heathrow recorded an 18.3% year-on-year decline in demand to 14.6 million passengers between January and March, while earnings before tax and interest fell by 22.4% to £315 million.
The airport insisted its financial position is "robust", with £3.2 billion in liquidity, which is "sufficient to maintain the business at least over the next 12 months, even with no passengers".
It is calling for the UK to lead the way in developing a common international standard for safe air travel.
Chief executive John Holland-Kaye said: "Heathrow is proud to serve Britain by remaining open for repatriating UK citizens and critical supplies of PPE (personal protective equipment)."