Transportation Secretary Sean Duffy said Friday’s four-hour ground stop was declared after maintenance work to upgrade an old copper wire to a high-speed fiber cable had caused “issues” with communication with airplanes and radar feeds.

“Either through contractor error or a faulty piece of equipment…it started flooding other routers in our air traffic control system,” Duffy told reporters.

In another embarrassment, Saturday’s news conference — where administration officials also appealed for more funds to upgrade outdated systems — was delayed due to technical problems with the audio feed.

Stocks fell in shaky trading on Wall Street Friday, but the market still posted its first winning week since early October.

The S&P 500 fell 0.4% Friday and closed with a weekly gain of 2.5%.

The Dow Jones Industrial Average rose 50 points, or 0.1%. The Nasdaq composite fell 0.9%.

Technology stocks were the biggest weights on the market. Nvidia shares fell again, a day after the AI industry was rocked by the resignation of CEO Jensen Huang. Oil prices were little changed. Treasury yields rose in the bond market. Stocks in Europe were mixed.

On Friday:

The S&P 500 fell 30.73 points, or 0.4%, to 7,561.67.

The Dow Jones Industrial Average rose 50.46 points, or 0.1%, to 52,347.55.

The Nasdaq composite fell 229.82 points, or 0.9%, to 25,136.27.

The Russell 2000 fell 8.57 points, or 0.3%, to 2,790.49.

For the week

S&P 500 is up 184.81 points, or 2.5%.

The Dow is up 1,061.82 points, or 2.1%.

The Nasdaq is up 556.85 points, or 2.3%.

The Russell 2000 is up 36.38 points, or 1.3%.

For the year:

The S&P 500 is up 716.17 points, or 10.5%.

The Dow is up 4,284.26 points, or 8.9%.

The Nasdaq is up 1,894.28 points, or 8.2%.

The Russell 2000 is up 308.58 points, or 12.4%.