Ken Giacobbe
Executive Vice President and Chief Financial Officer at Howmet Aerospace
Thank you, John.
Let's -- please move to Slide 5. Fourth quarter total revenue was up 4% year-over-year and flat sequentially. Commercial Aerospace increased to 44% of total revenue, which is an improvement sequentially, but far short of the pre-COVID levels of 60%. Commercial Aerospace recovery continued in the fourth quarter with Commercial Aerospace revenue up 13% year-over-year and 4%, sequentially, driven by the Engine Products segment and the narrow-body recovery.
Defense Aerospace was down 22% year-over-year and 4% sequentially, driven by customer inventory corrections and production declines for the Joint Strike Fighter. Commercial Transportation, which impacts both the Forged Wheels and the Fastening Systems segment was up 20% year-over-year, driven by higher aluminum prices. However, the market was down 1% sequentially as the market continues to be impacted by supply chain constraints at our customers, which is limiting commercial truck production.
Finally, the industrial and other markets which is composed of IGT, oil and gas and general industrial was down 2% year-over-year and 3% sequentially. Now, let's move to Slide six, which sums up the year nicely. Let's start with the P&L. For the full year, price increases were up year-over-year and in line with expectations, as they are primarily tied to long-term agreements.
Structural cost reductions were approximately $130 million, which exceeded our target of $100 million. Adjusted EBITDA margin for the year was 22.8%, which was an increase of 220 basis points year-over-year, despite $285 million of lower revenue. The fourth quarter exit rate was 23%. Adjusted earnings per share was $1.01 or 31% higher than 2020.
Moving to the balance sheet, our cash balance was healthy at $722 million. Adjusted free cash flow was a record $517 million, which was well above the guidance. Free cash flow conversion was 117% of net income, and if we exclude voluntary pension contributions of $28 million, adjusted free cash flow conversion was 123% of net income. Net pension and OPEB liabilities were reduced by approximately $275 million, while pension and OPEB expense, as well as the associated cash contributions were each reduced by approximately 54%. Net debt-to-EBITDA improved to 3.1 times.
Regarding capital allocation, we have taken a balanced approach. Capital investment projects for Forged Wheels at Hungary and Mexico are now essentially complete. Concurrently, we have been investing in automation projects in the Engines and Fasteners segments.
During the year, we paid down gross debt of approximately $845 million, with cash on hand and reduced annualized interest costs by approximately $70 million. We also reinstated the quarterly dividend of $0.02 per share of common stock in Q3 of 2021. Lastly, we repurchased approximately 13.4 million shares of common stock for $430 million, with an average acquisition price of $32.07 per share. To sum it up, during the year, we enhanced our profitability, strengthened the balance sheet, and we are balanced in our capital allocation.
Let's move to Slide 7 to briefly cover the segment results. Engine Products year-over-year revenue was 9% higher in the fourth quarter. Commercial Aerospace was 39% higher driven by the narrow-body recovery. Defense Aerospace was down 26% year-over-year, driven by customer inventory corrections and production declines for the Joint Strike Fighter. Operating profit increased 10% year-over-year and operating margin improved 20 basis points, despite adding approximately 150 employees in the fourth quarter, which now brings our total employees added since Q1 to approximately 950 employees.
Now let's move to Slide 8. As expected, Fastening System's year-over-year revenue was 3% lower in the fourth quarter. Commercial Aerospace was 15% lower, as we continued to experience production declines for the Boeing 787. Commercial Transportation was up approximately 46%. Year-over-year, Fastening Systems was able to maintain segment operating profit on $7 million of lower revenue. As a result, operating margin improved 50 basis points.
Now let's move to Slide 9. Engineered Structures' year-over-year revenue was 12% lower in the fourth quarter. Commercial Aerospace was flat, as the narrow-body recovery was offset by production declines for the Boeing 787. The Defense Aerospace market was down 26% year-over-year and flat sequentially. Year-over-year, Engine Structures was able to generate $3 million more in segment operating profit on $27 million of lower revenue, primarily due to permanent cost reductions and a favorable $2.5 million non-recurring adjustment related to a customer contract negotiation. As a result, operating margin improved 260 basis points.
Finally, let's move to Slide 10. Forged Wheels' year-over-year revenue was 15% higher in the fourth quarter. Approximately $28 million of the $31 million revenue increase was due to higher aluminum price pass-through. Pass-through of higher aluminum prices did not impact operating profit dollars, but unfavorably impacted operating profit margin by approximately 350 basis points. On a sequential basis, revenue and operating profit were essentially flat.
Commercial Transportation demand remained strong, but volumes continued to be impacted by customer supply chain issues. Aluminum prices were flat sequentially, resulting in minimal impact to sequential operating profit margin. One final comment on the segments, the incremental profit flow-through for the segments in Q4 was 30% year-over-year and can be found in the appendix. The 30% includes a 55% increase in aluminum prices year-over-year, which adversely impacted the incremental profit flow-through. If we adjust for aluminum prices, incrementals were above 70%.
Now let's move to Slide 11. We continued to focus on improving our capital structure and liquidity. In 2021, we took actions to lower our annualized interest costs by approximately $70 million through a combination of paying down gross debt by approximately $845 million with cash on hand and also refinancing higher cost debt with lower cost debt. Gross debt remains at $4.2 billion.
Net debt-to-EBITDA improved to 3.1 times, despite cash used for debt refinancing, share buybacks and dividends. All debt is unsecured and the next maturity is in October of 2024. Finally, our $1 billion revolving credit facility remains undrawn. Before turning it back to John to discuss the guidance, I'd like to point out a few items that you can find in the appendix. First, there's a slide in the appendix that covers special items in the quarter. Special items for the fourth quarter were a net charge of approximately $53 million, mainly driven by costs associated with non-cash pension plan settlement charges.
Second, there's a slide in the appendix that summarizes the share repurchases that occurred in 2021, as well as the share repurchases in January of 2022. Remaining common stock share repurchase authority sits at $1.25 billion as of February 1, 2022.
Finally, in the reconciliation of adjusted free cash flow, you will notice the cash receipts from sold receivables is zero dollars in the fourth quarter. As a result of restructuring our accounts receivable securitization program in Q3 2021, cash receipts from sold receivables will be zero going forward and the entire impact from the sale of accounts receivables will be in cash from operations. Therefore, starting with Q4 of 2021 and beyond, the definition of free cash flow will be simplified and be cash from operations less capex.
Please note that the net cash funding from the sale of accounts receivable has been $250 million since Q4 of 2020, which means that the sale of accounts receivables has neither been a source of cash or a use of cash in 2021.
So, with that, let me now turn it back over to John.