USAir Inc. yesterday reported record earnings for the third quarter and the first nine months of the year.

Ethyl Corp. reported increased profits, but Penril Corp. said its earnings for the fiscal year ended July 31 were down from the previous year.

Washington-based reported net earnings of $16.2 million (93 cents a share) in the third quarter, up 129 percent from $7.1 million (40 cents) in the third quarter of 1981, which was affected by the air traffic controllers' strike. Revenue for the third quarter totaled $331.7 million, up 23.7 percent from $268.1 million in 1981.

The airline reported record nine-month earnings of $47.1 million ($2.70) on revenues of $946.4 million, compared with earnings of $38.4 million ($2.41) on revenues of $816.1 million in 1981.

In the third quarter, the airline said it broke even and began to make money when it filled 52 percent of its seats; during the same quarter a year ago, it had to fill 57.5 percent of its seats to be profitable.

Ethyl Corp. of Richmond reported net income of almost $23 million ($1.13) in the third quarter, up 8 percent from $21.2 million ($1.06) in the year-previous quarter. The company, a diversified producer of chemicals, plastics and aluminum products said third-quarter sales declined 8 percent to $410.7 million, compared with $448.2 million last year.

For the first nine months of the year, Ethyl's net income totaled $68 million ($3.38) on sales of $1.2 billion, compared with earnings of $67 million ($3.36) on sales of $1.3 billion for the 1981 period.

Penril Corp. reported net income of $1.7 million (85 cents) in its fiscal year ended July 31, down from $2.3 million ($1.15) in the prior year. The Rockville-based firm, which produces data communications equipment, electric test and measurement instruments and high fidelity speakers, said revenue totaled $39.6 million for its latest fiscal year, compared with $40.1 million in fiscal 1981.

For the quarter ended in July, Penril reported net income of $289,000 (15 cents) on revenues of $10.4 million, compared with income of $544,000 (27 cents) on revenues of $10.6 million in the same period of 1981.

Contributing to reduced earnings were severe price reductions by some suppliers in the markets it serves, Penril said.

Family Entertainment Centers Inc. reported a third-quarter profit of $85,124 (6 cents) on sales of $3,364,811 from its group of Chuck E. Cheese Pizza Time Theatres in the District of Columbia, Maryland and Virginia.

A year ago, the fast growing company reported a loss of $55,401 (5 cents) on sales of $770,072 for the quarter. The company has grown from two stores a year ago to 12 after opening four during the latest quarter. Profits through nine months amounted to $7,940 (1 cent) on sales of $7,776,000, compared with a loss of $31,453 (3 cents) on sales of $1,599,118.

Noland Co., a wholesaler of mechanical equipment to the building trades, posted third-quarter profits of $833,500 (34 cents) on sales of $63.4 million, compared with $1.3 million (55 cents) and sales of $70.6 million in 1981. For nine months, Noland earned $2.1 million (86 cents), compared with $3.1 million ($1.26) last year. Sales dropped to $183.2 million from $199.7 million.