It is unknown at this point if Mrs Trump will attempt today to get to Philadelphia.
First lady Melania Trump took a seat, July 13, during a visit to The Royal Hospital Chelsea in central London.
Reports from inside the plane say Secret Service officers hopped up from their seats and rushed toward the front of the plane. A source described it as a "minor technical issue" and that the first lady was "fine".
A few minutes after takeoff, those aboard the plane observed a thin haze of smoke coming from the cabin and smelled something burning.
Press on the plane put wet towels over their faces when the smell became too strong.
The smoke eventually cleared and the smell dissipated.
In May, Trump launched her BE BEST awareness campaign, which is centered around children's health.
She was joined on her visit to Thomas Jefferson University Hospital by Health and Human Services Secretary Alex Azar.
Mrs Trump was to tour a neonatal intensive care nursery and speak at a conference on a new system that tracks infants suffering opiate withdrawal.