The ETG Group set a quarterly net sales and operating income record in the second quarter of fiscal '21, improving 11% and 9%, respectively.
These increases, principally reflect the impact from our profitable fiscal '20 and '21 acquisitions, as well as very strong organic growth of 19% for our other electronic products.
The Flight Support Group reported sequential growth in operating income and net sales in the second quarter of fiscal '21, and they improved 37% and 16% respectively, as compared to the first for fiscal '21.
Our total debt to shareholders' equity reduced and improved to 27.1% as of April 30, '21 and that compared to 36.8% as of October 31, '20.
Our net debt, which is total debt less cash and cash equivalents, of $199 million as of April 30, '21 compared to shareholders' equity ratio improved to 9.2% as of April 30, '21 and that was down from 16.6% as of October 31, '20.
And this provides HEICO with substantial acquisition capital in the balance of our $1.5 billion unsecured revolving credit facility as well as other available capital.
Our net debt to EBITDA ratio improved to 0.47 times as of April 30, '21, down from 0.71 times as of October 31, '20.
Cash flow provided by operating activities remained strong, increasing 2% to $210.1 million in the first six months of fiscal '21 and that was up from $205.9 million in the first six months of fiscal '20.
We do expect this acquisition to be accretive to earnings within the first 12 months following the closing.
The Flight Support Group's net sales were $429.6 million in the first six months of fiscal '21, as compared to $553 million in the first six months of fiscal '20.
The Flight Support Group's net sales were $230.3 million in the second quarter of fiscal '21, as compared to $252 million in the second quarter of fiscal '20.
The Flight Support Group's operating income was $61.3 million in the first six months of fiscal '21, as compared to $109.6 million in the first six months of fiscal '20.
The Flight Support Group's operating income was $35.5 million in the second quarter of fiscal '21, as compared to $47.5 million in the second quarter of fiscal '20.
The Flight Support Group's operating margin was 14.3% in the first six months of fiscal '21, as compared to 19.8% in the first six months of fiscal '20.
The Flight Support Group's operating margin was 15.4% in the second quarter of fiscal '21, as compared to 18.9% in the second quarter of fiscal '20.
The Electronic Technologies Group's net sales increased 9% to a record $466.6 million in the first six months of fiscal '21, up from $427.4 million in the first six months of fiscal '20.
The net sales increase in the first six months of fiscal '21 principally reflects our fiscal '20 and '21 acquisitions as well as organic growth of 1%.
The Electronic Technologies Group's net sales increased 11% to a record $243.1 million in the fiscal second quarter of '21, up from $219 million in the second quarter of fiscal '20.
The net sales increase in the second quarter of fiscal '21 principally resulted from our fiscal '20 and '21 acquisitions, as well as organic growth of 3%.
The Electronic Technologies Group's operating income increased 7% to a record $131.4 million in the first six months of fiscal '21, up from $123 million in the first six months of fiscal '20.
The Electronic Technologies Group's operating income increased 9% to $71.3 million in the second quarter of fiscal '21, as compared to $65.5 million in the second quarter of fiscal 2020.
The Electronic Technologies Group's operating margin was 28.2% in the first six months of fiscal '21, as compared to 28.8% in the first six months of fiscal '20.
The Electronic Technologies Group's operating margin was 29.3% in the second quarter of fiscal '21, as compared to 29.9% in the second quarter of fiscal '20.
Moving on to details, the diluted earnings per share, consolidated net income per diluted share was a $1.03 in the first six months of fiscal '21, and that compared to $1.44 in the first six months of fiscal '20.
Consolidated net income per diluted share was $0.51 in the second quarter of fiscal '21, as compared to $0.55 in the second quarter of fiscal '20.
Depreciation and amortization expense totaled $22.9 million in the second quarter of fiscal '21, that was up from $21.7 million in the second quarter of fiscal '20, and totaled $45.9 million in the first six months of fiscal '21, up from $43.3 million in the first six months of fiscal '20.
R&D expense increased to $34.2 million or 3.9% of net sales in the first six months of fiscal '21, and that was up from $33.1 million [Phonetic] or 3.5% of net sales for the first six months of fiscal '20.
R&D expense increased to $18 million or 3.9% of net sales in the second quarter of fiscal '21, and that was up from $16.8 million or 3.6% of net sales, second quarter fiscal '20.
Our consolidated SG&A expense were $161.2 million in the first six months of fiscal '21, as compared to $157.8 million in the first six months of fiscal '20.
Consolidated SG&A expenses were $83 million in the second quarter of fiscal '21, and that compared to $70.7 million in the second quarter of fiscal '20.
Consolidated SG&A expenses as a percentage of net sales increased to 18.2% in the first six months of '21, up from 16.2% in the first six months of fiscal '20.
Consolidated SG&A expense as a percentage of net sales increased to $17.8 million [Phonetic] in the second quarter of fiscal '21, and that was up from 15.1% in the second quarter of '20.
Interest expense decreased to $4.5 million in the first six months of fiscal '21, down from $8 million in the first six months of fiscal '20.
Interest expense decreased to $2.1 million in the second quarter of fiscal '21, and that was down from $3.8 million in the second quarter of fiscal '20.
Our effective rate in the first six months of fiscal '21 was 12%, as compared to 0.3% in the first six months of fiscal '20.
Our effective tax rate decreased to 19.5% in the second quarter of '21 -- fiscal '21, and that was down from 22.6% in the second quarter of fiscal '20.
Net income attributable to non-controlling interest was $11.5 million in the first six months of fiscal '21, and that compared to $13.4 million in the first six months of fiscal '20.
Net income to non-controlling interest was $5.8 million in the second quarter of fiscal '21, as compared to $5.5 million in the second quarter of fiscal '20.
For the full fiscal '21 year, we continue to estimate a combined effective tax rate and non-controlling interest rate of between 24% and 26% of pre-tax income.
One thing I want to mention that in the second quarter of fiscal '21, cash flow from operations was a 146% of reported net income.
So the net income was $70.7 million and the cash flow was almost $103 million.
As we discussed earlier, cash flow provided by operating activities increased 2% to $210.1 million in the first six months of fiscal '21, and that was up slightly from $205.9 million in the first six months of fiscal '20.
Our working capital ratio was 4.5 times, '21 as of April 30, compared to 4.8 times as of October 31, '21 [Phonetic].
Our days sales outstanding of receivables improved to 41 days as of April 30, '21, that was down slightly from 44 days as of April 30, '20.
No one customer accounted for more than 10% of net sales.
Our five -- top five customers represented approximately 23% and 24% of consolidated net sales in the second quarter of fiscal '21 and '20, respectively.
Inventory turnover rate was 153 days for the period ending April 30, '21 compared to 139 days for the period ended April 30, '20.
Despite the increased turnover rate, our subsidiaries has done an excellent job controlling inventory levels in the first six months of fiscal '21, and we believe that's appropriate to support expected future net sales as well as our increased backlog as of April 30, '21, which increased by $51 million to $895 million.
Given those uncertainties, we cannot provide fiscal '21 net sales and earnings guidance at this time.
We continue to estimate capital expenditures of approximately $40 million for fiscal '21.
I want to remind the listeners that a very high percentage of HEICO members are HEICO shareowners through their 401(k) plans.

Summary:
Consolidated net income per diluted share was $0.51 in the second quarter of fiscal '21, as compared to $0.55 in the second quarter of fiscal '20.
Despite the increased turnover rate, our subsidiaries has done an excellent job controlling inventory levels in the first six months of fiscal '21, and we believe that's appropriate to support expected future net sales as well as our increased backlog as of April 30, '21, which increased by $51 million to $895 million.
Given those uncertainties, we cannot provide fiscal '21 net sales and earnings guidance at this time.